Iris

IRIS (iris) is the anterior part of the vascular tract of the eye and represents a circular disk. It is located behind the cornea and in front of the lens, separating the anterior chamber of the eye from the posterior. In the center of the iris, somewhat inward, there is a round opening, the pupil (pupilla), which can constrict and dilate. The edge of the iris forming the pupil is free and is called the pupillary edge (margo pupillaris). It is bordered by a black stripe of pigment, especially noticeable against the gray background of a cloudy lens. The edge of the iris adjacent to the ciliary body is known as the ciliary edge (margo ciliaris), and is sometimes also referred to as the root or base of the iris. This edge is attached by means of the pectinate ligament (ligamentum pectinatum) to the place where the sclera transitions into the cornea. With average pupil constriction, the vertical diameter of the iris is 12 mm, and the horizontal is 12.5 mm. Its thickness, greatest in the area of the small arterial circle, varies from 0.3 to 0.6 mm. From here, the profile of the iris forms a gradual slope both toward the pupil and toward its base, where it has the least thickness, sometimes reaching 0.05 mm. A distinction is made between the anterior surface of the iris, which limits the anterior chamber, and the posterior surface, which faces the posterior chamber of the eye and lies to a greater or lesser extent against the anterior surface of the lens. At the border of the inner and third of the anterior surface of the iris, there rises a thickening of tissue, arranged concentrically to the pupillary edge and containing a vascular plexus known as the small arterial circle of the iris (circulus arteriosus iridis minor). This formation, because of its fringed edge, is also called the iris mesentery, in turn divides it into two parts: the central narrow, surrounding the pupil, the pupillary part, and the peripheral wider, ciliary part. The iris is positioned in the eye such that its pupillary part protrudes more forward than the ciliary part, as a result of which the eye as a whole acquires the appearance of a low truncated cone, the apex of which corresponds to the pupil. The shallower the anterior chamber, the lower this cone. In the absence of the lens (aphakia), which serves as a support for the iris, the latter has the ability to lie in one plane, and trembles, creating a picture so-called iridodonesis, which can be especially well observed with sharp head movements. The anterior surface of the iris has a delicate pattern, a relief formed by elevations and depressions. Among the former are the trabeculae, extending radially, which contain vessels. Between the trabeculae are triangular or rhombic depressions, crypts, concentrated mainly in the area of the small arterial circle. Similar depressions, but narrower, are found in the ciliary part of the iris, although here they are very small and covered by the advancing sclera. In the ciliary part of the iris, it is necessary to note several concentric, little-pigmented grooves of contraction. They occur because when the pupil dilates, the surface of the iris folds and in the area of each groove a fold forms. One of these folds lies approximately at the border of the middle and outer third of the iris, is more constant and is called the large circle of the iris (circulus iridis major). The posterior surface of the iris, except in cases of albinism, is always black, as it is covered with pigment. It has 2 systems of folds: a) radial and b) circular. From the pupillary edge, the radial folds are limited by numerous small grooves, which, bending together with the pigment epithelium through the edge of the pupil, form a notched border. Another type of radial fold begins at a distance of 1.5 mm from the pupillary edge. These folds are first limited by narrow and deep grooves, and then toward the ciliary edge by wider and shallower ones. The circular folds are separated from each other by delicate circular grooves and are located only in the area of the second type of radial folds. The color of the iris (in simple terms - eye color) varies from light coloring (blue and gray) to dark (light-brown, dark-brown and almost black) and depends on the amount of pigment: the iris of an albino is completely devoid of it, a blue iris has pigment only on the posterior surface, a brown or brown iris contains pigment in both the connective tissue layer and on the posterior surface. A normal iris does not always have uniform coloration over its entire surface. Thus, the area of the sphincter of the pupil is often colored differently than the rest of the surface. On it may be found slightly elevated black spots, moles (naevus iridis). Sometimes the color of the iris is different in both eyes - heterochromia iridis (see Heterochromia). Depending on the process of thickening of the stroma and accumulation of pigment in it, the color of the iris in humans is established only several years after birth. From an embryological point of view, the iris must be divided into two parts: retinal (cerebral) and mesodermal. The first is represented by two layers of pigment epithelium, which formed on the 3-4th month of embryonic life from the anterior wall of the eye cup. The second part is formed from the richly vascularized mesenchyme located in front of the lens. The latter splits into 2 layers: the anterior forms the basis for the substance of the cornea, and the posterior turns into the stroma of the iris. The slit that appeared between these layers is modified into the anterior chamber. The posterior layer of mesenchyme covers the pupillary area with a membrane and is known as the pupillary membrane. This embryonic membrane only undergoes regression in the last months of embryonic life, making the pupil free. In rare cases, small remnants of it persist throughout life, manifesting in the form of so-called persistent pupillary membrane. Starting from the iris mesentery (by no means from the edge or stroma of the iris), remnants of the embryonic membrane in the form of threads attach to the lens, only spanning across the pupil and giving it the ability to constrict and dilate. The embryonic rudiment of the sphincter of the pupil is found already at the end of the 2nd month of embryonic life, and it is formed from epithelial cells in the area of the pupil, whereas the dilator of the pupil owes its origin to the anterior layer of the eye vesicle and its first traces in humans appear in the 6-7th month of intrauterine life. In the history of eye development, it is necessary to note the formation of the embryonic fissure. It arises as a result of the inward bending of the lower wall of the eye vesicle under the pressure of mesoderm simultaneously with a similar inward bending of the anterior wall of the eye vesicle. This fissure eventually closes, and its delayed closure or absence thereof usually leads to the formation of a defect known as a coloboma of the iris (see Coloboma). When histologically examining the iris, the stroma must first be distinguished in it, consisting of loose connective tissue, richly supplied with radially running blood vessels. Being supplied with a thick adventitia, they originate from the root of the iris, from the large arterial circle (circulus arteriosus iridis major). Reaching the iris mesentery, the vessels form here not quite a closed circle. In the area of the sphincter of the pupil, the vessels break down into capillaries, which, by the way, are few in the iris. In addition to vessels, nerves pass through the stroma of the iris: motor nerves for the musculature of the iris and sensory nerves from the trigeminal nerve, also clothed in a thick neurilemma. The space between the nerves and vessels is dotted with star-shaped, branched, pigmented cells - chromatophores. These cells lie especially densely on the anterior surface of the iris, isolating its anterior stromal layer, the anterior limiting layer, and in the crypts this layer is absent. Crypts are openings extending into the depth of the iris and communicating with the anterior chamber. Near the pupil, in the thickness of the stroma, is located the sphincter of the pupil (sphincter pupillae), which has the typical structure of smooth muscle. This muscle has the appearance of a round flat ribbon, 1 mm wide, and is innervated by the inner branch of the oculomotor nerve through the ciliary ganglion. On the posterior surface of the iris is located the dilator of the pupil (dilatator pupillae), innervated by the sympathetic nerve from the plexus caroticus. The latter muscle is formed by cells of a special kind, not found anywhere else in vertebrates. They have a nucleus-containing pigmented body, which lies on the contracting part of the cells, consisting of myoglio-fibrils. On cross-sections of the dilator of the pupil, two parts are distinguished in it: the anterior, unpigmented, without nuclei, thinly striated layer, known as Bruch's posterior limiting membrane, and the posterior, consisting of nucleus-containing and pigmented spindle-shaped cells, otherwise called the anterior pigment layer. From the dilator of the pupil to its sphincter go individual bundles of fibers, connecting on separate areas the two muscles. Behind the anterior pigment layer lies the posterior pigment layer, the pigment epithelium of the iris.

It is a slightly elevated layer of large, cylindrical, heavily pigmented cells, and is easily separated from the dilator of the pupil both in microscopic preparations and when adhesions of the iris with the anterior capsule of the lens, so-called posterior synechiae, are torn. Being a continuation of the inner layer of the ciliary epithium and the termination of the choroid, the pigment epithelium also extends to the anterior surface of the iris, forming the pupillary border. The iris participates in the formation of the angle of the anterior chamber, which is very important in the physiology and pathology of the eye department. In general, this angle is formed by the convergence of the cornea and iris, and a more detailed examination of it provides grounds for highlighting a special loose connective tissue here, which is actually the nearest boundary of the angle of the anterior chamber, acquiring the name of the supporting frame of the angle of the anterior chamber, the pectinate ligament (lig. pectinatum). The latter on meridional sections of the eye has the shape of a triangle, the acute apex of which passes into Descemet's membrane. Its outer side partially lies against the cornea, serving as the wall of Schlemm's canal. The base of the described triangle borders the sclera and ciliary muscle, and then the fibers of the pectinate ligament go along the anterior surface of the ciliary body and disappear at the root of the iris. At the same time, the inner side of this ligament is turned toward the anterior chamber. The collagen and elastic fibers of it form crossbars covered with endothelium, and the spaces between them are known as Fontana's spaces. The latter is filled with aqueous humor and is in direct connection with the angle of the anterior chamber. Between Schlemm's canal and Fontana's space, according to many authors, there is no direct communication. The physiology of the iris is mainly reduced to participation 1) in the nutrition of the eye together with other parts of the vascular tunic; 2) in the secretion of chamber fluid together with the ciliary body; 3) in the exchange of fluids of the eye and finally 4) in the optical play of the pupil. The iris performs its first function thanks to the abundance of blood vessels in it, from which aa. ciliares postici longae, numbering 2, pass between the choroid and sclera, ultimately forming the circulus arteriosus major. The formation of the latter is facilitated by aa. ciliares anticae, which originate from the arteries of the 4 rectus muscles. These arteries pierce the sclera near the edge of the cornea. Venous blood from the iris flows into the vortex veins (see table to the article Eye, fig. 3, schematic section in the horizontal plane of the eyeball). As for the secretion of chamber fluid, at present the majority of ophthalmologists do not deny the role of the iris in this process, but shift the center of gravity to the ciliary body. If the iris participates little in the secretion of chamber fluid, it has great importance in the absorption from the anterior chamber. Thus, blood from the anterior chamber quickly disappears where it covers the iris, while on the capsule of the lens in the pupillary area or coloboma it remains for a long time. This phenomenon is explained by the presence in the iris of crypts communicating with the anterior chamber. The play of the pupil, which changes the volume of the crypts, especially facilitates the rapid exchange of fluid between the tissue of the iris and the anterior chamber. The iris acquires important significance in the process of outflow of intraocular fluids, since the latter occurs by filtration from the angle of the anterior chamber through Fontana's space into Schlemm's canal. Obliteration of the angle of the anterior chamber can lead to glaucoma, in which such blockage is often anatomically confirmed [see Glaucoma (figs. 3 and 4)]. The angle of the anterior chamber can be obliterated due to independent inflammation around Schlemm's canal, stagnation in the veins of the ciliary body, sclerosis of the fibers of the pectinate ligament, reduction of the pericapsular space, etc. Even dilation of the pupil, accompanied by an increase in intraocular pressure, can cause obliteration of the angle of the anterior chamber. 2»2 ^; The optical play of the pupil is of great interest, thanks to which the amount of light entering the eye is automatically regulated. A luminous point sends rays in all directions, however, only a very narrow cone of rays enters the eye, the base of which is the pupil and the apex is the given point. A significant amount of circles of light scattering, reducing the clarity of vision, is due to peripheral rays that form a large angle with the optical axis of the eye. There are especially many such rays from nearby objects, and even a small displacement of the latter affects the clarity of vision. This drawback is corrected by the pupil, which performs the role of an aperture diaphragm, cutting out a cone of rays of a certain size and eliminating lateral rays. The number of rays entering the eye is directly proportional to the square of the diameter of the pupil. With insufficient illumination, dilation of the pupil (mydriasis) occurs and a large number of light rays enter the eye, with bright illumination, on the contrary, narrowing of the pupil (miosis) occurs and the eye is protected from the blinding effect of light. The most favorable conditions for vision are created with a pupil width of 3 mm, since with a wider pupil the eye is dazzled, with a narrower one the diffraction of light increases and the image is insufficiently illuminated. Therefore, the application of an artificial diaphragm to an atropinized eye improves vision, while in tabetics, even without changes in the fundus of the eye, decreased vision may be associated only with a small diameter of the pupil. The size of the pupil is influenced by the blood filling of the iris, so with its hyperemia (iritis) we have narrowing of the pupil. Loss of elasticity of the iris in old age leads to a sluggish reaction of the pupil. Posterior synechiae, injuries and tumors of the iris can interfere with the proper functioning of the pupil. Similarly, anterior synechiae, adhesions of the iris with the cornea after ulcers and injuries of the latter affect the mobility of the pupil, displacing it from the normal position. The size of the pupil in adults varies from 2.5 to 4.5 mm, and they distinguish the relative diameter of the pupil, observed in scattered light and with both eyes open, and the absolute one - with the other eye closed. A persistent decrease in the diameter of the pupil below 2 mm and an increase above 6 mm is an abnormal phenomenon. For measuring the diameter of the pupil there are pupillometers, of which Haab's pupillometer is a cardboard ruler with images of black circles differing from each other by 0.5 mm in diameter. The corresponding circle can be used to determine the diameter of the pupil. Narrowing of the pupil can be caused either by contraction, spasm of the sphincter (miosis spastica), or paralysis of the dilator (miosis paralytica). In the first case, under pathological conditions, miosis can be caused by inflammatory processes in the iris (in iritis), poisoning (morphine, etc.), intracranial disorders (initial period of meningitis), hysteria, etc. In the second case, we have either peripheral damage to the dilator (in contusion of the eye) or compression and damage to the cervical sympathetic nerve (myelitis, syringomyelia), etc. In turn, dilation of the pupil is observed in 2 forms: mydriasis spastica and mydriasis paralytica. The first is caused by intraocular irritation of the dilator (cocaine, etc.), weak compression and irritation of the ciliospinal center (meningitis), excitation of the brain (epilepsy), hysteria, etc. The second is caused by paralysis of the sphincter (atropine), increased intraocular pressure, trauma, poisoning (chloroform), finally paralysis of the oculomotor nerve. See also Anisocoria, Pupillary fibers, reflexes, centers. Various pupillary symptoms are an expression of either 1) a local pathological process in the eye (action of atropine, eserine, iritis, glaucoma, diseases of the visual nerve apparatus of the eye, especially in connection with decreased vision), or 2) a general suffering of the whole body (post-diphtheric mydriasis, botulism, morphinism), or 3) accompany diseases of the central nervous system (tabes dorsalis-miosis, irregular shape of the pupil, its unevenness in both eyes-Argyll-Robertson symptom; progressive paralysis-absolute immobility of the pupils; syphilis of the brain-ophthalmoplegia interna). Among the rare pupillary reactions is pupillotonia, or myotonic reaction of the pupil (see Myotonia), and neurotonic reaction. In the latter, the pupil narrows on light and remains in this narrowed state for a long time after the cessation of light irritation, slowly expanding to its original size. The pathology of the iris is most often caused by disease of the whole organism, which necessitates careful general examination to establish the etiological factor and the appropriate combination of general therapy of the main suffering with local effects on the process in the eye itself. Being part of the vascular tract, the iris is involved in the pathological process both from the side of the ciliary body, giving a picture of iridocyclitis (see.

Iritis) as well as from the side of the vascular tunic, when iritis passes into iridochoroiditis (iridochoroiditis). The latter in the form of so-called primary traumatic endophthalmitis often accompanies penetrating wounds of the eye and is accompanied by conjunctival and ciliary injection, hyperemia of the iris and slight exudation. With prolonged course, this form passes into plastic endophthalmitis, when the exudate turns into connective tissue strands inclined to shrinkage, whereby both the iris and the lens are pulled backward. If the trauma is complicated by infection, the fluid of the anterior chamber becomes cloudy and the color of the iris changes. After the disappearance of the exudate, the iris appears pierced by newly formed vessels, and the pupil is covered with a dense membrane. When infection penetrates into the vitreous body, a change in the color of the iris, posterior synechiae, and in the depth of the pupil a yellowish-white opacity are observed. All this in total creates the picture of purulent iridochoroiditis, which usually ends in atrophy of the eye. Purulent iridochoroiditis sometimes arises endogenously (purulent endophthalmitis), when the causative agents of inflammation enter the eye with the blood flow, forming capillary emboli. At the beginning of such iridochoroiditis, dense opacities of the vitreous body are observed, and in the subsequent time, phenomena from the side of the iris are added to them: change in its color, posterior synechiae, pupillary effusion, pus in the anterior chamber. In the outcome of the disease, connective tissue strands form in the vitreous body, giving a picture of amaurotic cat's eye with a clearly visible light yellow reflex in the depth of the pupil. The iris also participates in sympathetic iridochoroiditis, in which it changes in color, thickens and is pierced by dilated blood vessels. The exudate between the iris and the lens organizes and attaches the pupil margin to the latter, forming a circular synechia (secclusio pupillae) (see Iritis, separate plate, fig. 4). The exudate on the anterior capsule of the lens turns into a membrane covering the entire area of the pupil (occlusio pupillae). Finally, the attachment of the entire posterior surface of the iris to the anterior capsule of the lens with the formation of a complete posterior synechia may occur. The presence of posterior synechiae separates the anterior and posterior chambers of the eye, disrupts the proper circulation of fluids in the eye and leads to an increase in intraocular pressure, atrophy of the iris, clouding of the lens and finally atrophy of the eyeball. The participation of the iris in diseases of the cornea is very frequent (see Keratitis). Atrophy of the iris may first manifest in the form of atrophy of the anterior border layer, when the radial vessels become clearly visible. The disappearance of chromatophores makes the blue iris gray, and the brown one - ash-gray. The pigment of the iris breaks down and covers the anterior surface with fine dust, sometimes forming a suspension in the anterior chamber and clogging its angle. Atrophy of the iris can go to the disappearance of all its layers and the formation of holes in it, through which a red reflex is visible from the bottom of the eye. Sometimes atrophic processes in the iris can be combined with the proliferation of fibrous interstitial tissue. Causes of iris atrophy: old age, mechanical stretching during ectasia of the eyeball and fixation of the pupil with synechiae, past inflammation, increased intraocular pressure, etc. Among the injuries of the iris, one must mention the tearing off of a part of it from the root, so-called iridodialysis, in which there is a black hole at the edge of the cornea. This hole, externally limited by the edge of the sclera, and internally by the torn-off root of the iris, takes the shape of a circular segment, giving a red reflex when illuminated with an ophthalmoscope. The pupil loses its roundness, being beveled toward the side of the injury. Sometimes the injury to the iris manifests in the form of radial tears of the pupillary margin, which results in traumatic mydriasis. Traumatic injuries to the iris are very often accompanied by hemorrhage into the anterior chamber, hyphema (see Hyphaema). The prolapse of the iris (prolapsus iridis) has great practical significance, as it creates a threat of serious consequences: adhesion of the iris to the scar, secondary glaucoma, the occurrence of secondary infections and even the possibility of sympathetic inflammation. This situation also forces one to particularly carefully suture the iris during various operations or to remove it. More often, the prolapsed iris is removed and the wound is covered with a conjunctival flap taken from a neighboring area of the eyeball. Tuberculosis of the iris, syphilis of the iris - see Iritis. Tumors of the iris are represented by serous cysts, sarcoma and melanoma. Serous cysts have a benign course. Their walls are formed by a thinned iris. Filled with transparent fluid, serous cysts of the iris most often occur after penetrating wounds of the eye from displaced epithelial cells and grow either more forward or more backward. Similarly, trauma to the eye is responsible for the origin of those so-called pearl cysts of the iris with a pasty content resembling lard. To avoid obstruction of the outflow pathways and an increase in intraocular pressure, the cysts must be removed by means of iridectomy. Melanomas of the iris are benign tumors and have the appearance of darkish small formations originating from the vascular layer or the anterior border layer. They rise somewhat above the level of the iris and consist of chromatophores. Sarcoma of the iris already has a malignant course. It most often begins with pigmented spots that grow slowly. Subsequently, these spots begin to rise above the surface of the iris. Increasing in size, the tumor more and more fills the anterior chamber, inflammatory symptoms and glaucoma appear. Vision, which was normal at the beginning of the disease, gradually falls. With a small size of the tumor, especially in the initial stage, one can try to remove it by means of iridectomy, however, significant growth of the tumor and mainly its transition to the ciliary body is an indication for the removal of the eyeball. It is interesting to note Murzin's proposal to use for the removal of iris tumors an opening in the cornea made with a trephine by Hippel, whereby the circle of the cornea is not completely separated from it, but is connected to it like a valve. The most typical and widespread surgical intervention on the iris must be recognized as the excision of a part of it, iridectomy (see). It is performed both with the aim of lowering intraocular pressure and for the formation of an artificial pupil. The latter goal is also pursued by the operation of incision of the iris without removal of a part of it - iridotomy. This operation is usually performed on aphakic eyes, in which, due to postoperative iridocyclitis, a dense diaphragm has formed separating both chambers and consisting of adhesed together iris, exudative membrane and secondary cataract. After puncturing the cornea with a Graefe knife, the diaphragm is incised vertically to the direction of greatest tension. Due to its density, the diaphragm may offer significant resistance, in which case its incision with de Wecker's forceps-scissors is indicated. With a spear-shaped knife, an incision is made in the cornea along the limbus, after which forceps-scissors are introduced into the anterior chamber in such a way that the sharp blade pierces the iris and is located behind it, while the other blade lies over it. Then the scissors thus opened are advanced somewhat deeper, and by closing their blades the incision of the diaphragm is achieved. Instead of one, two incisions can be made in the form of the Roman numeral V and the piece of diaphragma outlined by them is removed from the anterior chamber, so that a combination of iridotomy and iridectomy is obtained. After iridotomy, a relapse of iridocyclitis is possible, which prompts one to proceed to this operation only after the disappearance of all signs of irritation. In the presence of a lens and to avoid injuring it, iridotomia extraocularis is used, when through an incision made in the limbus, the iris is extracted outward and is incised from the pupil toward its ciliary edge. Among other operations on the iris, one must note iridodesis and iridencleisis, proposed at one time for optical purposes. The latter was achieved by displacement of the natural pupil to the side due to the incarceration of the iris in a wound made on the periphery of the cornea or in the sclera. In this position, the iris was held either by a silk ligature (iridodesis) or simply pinched between the edges of the wound (iridencleisis). Such incarceration of the iris, especially in a scleral wound, can lead to iridochoroiditis and even sympathetic inflammation. In recent years, as antiglaucomatous operations, iridencleisis according to Holth and iridotasis according to Borthen have been recommended. Iridencleisis is proposed in the following form. Retreating 8-10 mm from the upper edge of the cornea, and parallel to it, an incision is made in the conjunctiva, which is then dissected downward, not reaching the limbus by 1 mm. With the point of a spear-shaped knife, placed exactly in the vertical meridian, an incision is made in the sclera.

In this incision, the iris is pulled out with iris forceps at the sphincter and is dissected from the pupil to the root. A complete coloboma results, both lobes of which are drawn into the scleral wound and incarcerated therein. Iridotomy consists in that after the conjunctival flap is dissected, a corneoscleral incision 4-5 mm long is made with a spear-shaped knife. With iris forceps, the iris is grasped, pulled into the wound opening, where it remains incarcerated, being held in this position and covered with conjunctiva, similar to subconjunctival prolapse of the iris. Of interest is the surgical intervention by Golovin in iridodialysis: with a spear-shaped knife, a small incision is made at the limbus, and the iris, grasped by iris forceps introduced into the anterior chamber, is seized by its edge, torn off, and incarcerated in the wound. On the other hand, iridodialysis was artificially reproduced for optical purposes in cases of pupil occlusion. For this purpose, Wecker made an incision in the cornea with a spear-shaped knife, the point of which was simultaneously injected into the iris. With two incisions, using scissors introduced into the anterior chamber, a flap of the iris was cut out, which was then torn off at its root. P. Arkhangel'skii. The pupil from a medico-legal standpoint. The postmortem condition of the iris has some significance for medico-legal examination. The size of the pupils in a corpse rarely exceeds 7 mm and is less than 2½ mm in diameter. Some anisocoria and unequal sizes in the vertical and horizontal diameters within 0.5 mm are observed quite frequently. After death, with a drop in intraocular pressure and a decrease in the amount of fluid in the anterior chamber of the eye, the iris loses its elasticity and the pupil easily changes shape from pressure on the eye. This postmortem property of the iris can be used to determine the time of death. The question to what extent and how often the postmortem size of the pupils reflects their antemortem condition remains unresolved. During agony, the pupils change rapidly and at the moment of death often do not correspond to what was noted during clinical observation. Anisocoria that existed during life may, but by no means always, be preserved in the eyes of the corpse. If one eye of the corpse remains open, the pupil of this eye is usually significantly narrower than that of the other, closed eye. This narrowing is explained by a decrease in the amount of aqueous humor in the anterior chamber due to increased evaporation on the uncovered eye. Artificial evacuation of fluid from the anterior chamber can cause a sharp narrowing of the pupil, and conversely, the introduction of fluid into the anterior chamber causes its dilation. Placzek established a certain regularity in the postmortem fluctuation of pupil size. Just before death, the pupils constrict sharply, and at the moment of death they dilate strongly. In the first hours after death, a gradual narrowing occurs, reaching its maximum within 6-12-24 hours. Then follows some dilation. Placzek's observations have been confirmed by Albrand and Willer. Postmortem narrowing of the pupils often does not occur at the same rate on different eyes of the same corpse. Then postmortem anisocoria arises. According to Placzek's data, poisoning with atropine, eserine, cocaine, as well as the transection of the cervical sympathetic nerve or its irritation in experiments on animals, have no effect on the regularity of postmortem changes in pupil size. However, Willer was able to observe that atropine, instilled into the conjunctival sac shortly before death, noticeably delayed the subsequent narrowing of the pupils. The postmortem rigor of the smooth muscles of the iris is considered the cause of the variability of postmortem pupil size. This explanation is hardly correct, since these muscles long after death retain their specific irritability, which is incompatible with the assumption of their postmortem rigor. Thus, Groenow observed constriction and dilation of the pupils in corpses after the introduction of pilocarpine and atropine into the conjunctival sac. Rusakov found that by injecting a solution of adrenaline and pilocarpine into the anterior chamber with a syringe, a specific pupillary reaction can be obtained within 24 hours after death. In this case, for each of the mentioned medications, two phases of action are observed. The first, occurring 5-15 seconds after injection, corresponds to what is known for the iris of a living person and causes a change in pupil diameter of 2-3 mm within 15-30 seconds. The second phase of action consists of the reverse movement, and the pupil returns to its original size within one or several minutes. Sometimes the second phase occurs an hour or more after injection. Insulin acts similarly to pilocarpine. An emulsion of the adrenal glands, prepared ex tempore during autopsy, causes an effect identical to that of pharmaceutical adrenaline. Application of the positive pole of an electric battery to the area of the corneal ring causes dilation of the pupil, while the negative pole causes constriction. Upon removal of the electrodes, the iris returns to its original position. The variability of pupil width under the influence of electricity persists for 5-6 hours after death. It must be assumed that in the postmortem state, not only the tone of the iris muscles but also the degree of swelling and deswelling of its stroma, occurring under the influence of postmortem changes in it, play a role in the iris. The width of pupils in corpses as a diagnostic sign in poisonings has only very relative significance, since postmortem changes in the iris do not always occur identically and at different rates. This explains the contradictory statements of toxicologists about the size of pupils in persons who died from poisonings. According to observations of the Sklifosovsky Institute of Emergency Aid, in cases of morphine poisoning, myosis was not noted in the eyes of the corpses. Similarly, there was never strong dilation of the pupils in people who died from botulism, despite the sharp and persistent mydriasis observed in them during life. Measurements of pupils in corpses can be made with a thin millimeter ruler. This method is quite inaccurate. Bliedung constructed a special pupillometer that allows detecting changes up to 0.1 mm.

A. Rusakov.

G. Karamanenko. Solving problems of R. in biology reflects those general philosophical premises on which this idea is based, as was indicated above. The most important question here is the discovery of the source of R., and around the various solutions to this question group the most common, at times opposite to each other, points of view. In relation to ontogenetic R., the search for its source was usually carried out by means of the so-called causal-analytical method, which to this day remains almost the only method of research in the field of mechanics of R. This branch of biology owes its origin and first steps, as well as the substantiation of basic principles, to Wilhelm Rou; it was he who laid the foundations of the causal-analytical method in the doctrine of the individual's R. 'The only, universal method of our science,' writes Rou, 'is the causal, consequently analytical method.' The definition that Rou gave to the category of cause has its source in the views of Spinoza and Kant and must be characterized as mechanistic. The cause of a phenomenon, according to Rou, is an impulse external to the phenomenon; analysis dissects the organism into external components or factors relative to each other, with one of them being declared the cause or determining factor in the emergence, preservation, or disappearance of another component, a group of them, or finally the entire system. Thus, the source of R. is contrasted with the developing system, and the process of R. is interpreted not as necessarily following from the previous state of the system. Thereby the possibility of uncovering the real driving forces of the process of R. is lost, and the solution of the question is reduced to the establishment of a possibility that does not admit of convincing verification. Let us clarify this with an example. The question is raised as to what is the source of the skeletal parts in the regeneration of a limb (e.g., in a newt). It is legitimate to assume that such a source is served by the skeletal elements remaining in the amputation stump. To test this hypothesis, the bones are removed from the amputated limb along with the corresponding girdle. The experiment shows that such a boneless stump gives regeneration of a^-limb provided with a skeleton. From this it is concluded that pre-existing skeletal parts are not in a causal relationship with the newly arising ones. However, this conclusion would be premature. The possibility of normal regeneration in the absence of skeletal parts in the residual organ does not yet indicate that under normal conditions bone does not participate in the regenerative process. It is quite legitimate to assume that the removal of bone leads to a completely different course of the entire process compared to what occurs in regeneration in the presence of a skeleton. The lack of certainty in the validity of conclusions obtained by causal analysis depends on the fact that in all cases one has to operate only with possibilities, and not with the elucidation of the real relationships existing in the process of R. Thus, the establishment of the necessity of any component for the course of the process of R. is only of a formal character, i.e., although the corresponding reasoning is flawless in form, it remains unknown whether this is actually the case. When Rou pointed out the impossibility of movement without an external impulse, he was in essence repeating the thought already expressed by Aristotle. The latter asserted that none of the natural bodies can move itself; each receives an impulse to move and in turn transmits it to another; therefore in every movement we have a pair: the mover and the moved. The fallacy of causal analysis also lies in that it leads to the establishment of a continuous, infinite series of causes and effects, which leads the researcher away from the object of study instead of immersing him in its essence. The internal contradiction of the infinite causal series is expressed by Kant in his 4th antinomy of pure reason. Kant sees no way out of this antinomy, because 'on the one hand, the causal series cannot be infinite—there must be a last member in the series, independent of anything else, something existing through itself—on the other hand, as soon as you try to define such a last unconditional necessary member, a contradiction immediately arises: everything that can be given is not the last, the understanding cannot get along without asking about the cause' (Paulsen). The clearest expression of the mechanistic understanding of causality was given by J. S. Mill in his 'Four Methods of Experimental Investigation.' The second of these methods, the method of single difference, is essentially the basis of causal analysis. The R. of many sex characteristics in vertebrate animals is attributed to the secretory activity of the sex glands. The attempt to establish the source of changes in the sex glands leading to the production of the hormone led to the doctrine of vitamin E, or the reproduction vitamin, entering the body with food. Further causal-analytical study of this question must obviously deal with the source of the appearance of this vitamin in wheat germ, lettuce leaves, and other plants where this vitamin occurs. In this example, the inevitability of moving away from the phenomenon under study (development of sex characteristics) instead of penetrating into its essence is particularly clear. When the phenomenon is dissected into individual components, their internal connection is broken and they thus turn out to be external to each other. The analytical study of the phenomena of R. usually seeks the source of changes in the action of one component on another. In this case, the phenomenon appears before the researcher in a frozen state, outside of movement. The task, however, is to try to understand the relationships that develop in the process of R. itself. 'The decomposition of nature into its separate parts,' writes Engels, '...was the basis of those giant successes by which natural science was marked in the last four centuries. But this same method of study has left us with the habit of taking things and phenomena of nature in their isolation, outside their great general connection, and for this reason not in motion, but in a state of rest, not as essentially changing, but as eternally unchanging, not as living, but as dead. Transferred by Bacon and Locke from natural science to philosophy, this worldview ^created the characteristic narrowness of the last centuries: the metaphysical way of thinking' ('Anti-Duhring'). The study of the problem of R. in biology requires the search for new paths, free from the objections which metaphysical theories deserve, in particular the causal-analytical method characterized above. These new paths of research will be fruitful only on the condition of applying to the study of R. the methodology of dialectical materialism. Only the consideration of R. as the unity of opposites, as the realization of an internally contradictory relationship in a developing system, will show a way out of the crisis of metaphysical thinking in which modern bourgeois science is trapped. The methodology of dialectical materialism has been developed by the founders of Marxism as a general worldview; it has been developed as a private methodology in its application to the development of social forms. The creation of a private methodology for biology, which will have access to the concept of R. in its true meaning, presupposes first of all a critical revision of old views and a reassessment of the previously accumulated factual material (see Ontogenesis, Organism, Organ-organogenesis, Postembryonic development, Preformation, Phylogenesis, Evolutionary teachings, Epigenesis).

l. Blyakher.