Depression in Biology

DEPRESSION IN BIOLOGY, the lowering of the normal course of life functions in protozoa, especially the normal rhythm of their reproduction. This phenomenon was first studied by R. Hertwig, who found that during the cultivation of certain rhizopods and infusoria, periods of enhanced nutrition, growth, and reproduction are replaced—without visible causes—by periods of depression (Calkins, 1902), when all these functions are sharply reduced. Depression can also be expressed in the appearance of ugly forms, in the dwarfing of individuals, and so forth. Depression can also be caused artificially by the most diverse factors: starvation, overfeeding, rapid transitions from the former to the latter, sharp temperature drops, the accumulation of dissimilation products in the culture fluid, and the like. Hertwig found that the onset of periods of depression is associated with hypertrophy of the nuclear apparatus, in other words—with a violation of the normal volumetric ratios between the nucleus and the body of the protozoan (nuclear-cytoplasmic relation). However, individuals in a state of depression can recover from it through the regulation of their nuclear apparatus, which occurs in the process of conjugation or in connection with encystment, as a result of which normal morphological and physiological relations are restored. Recent studies (Jennings, Woodruff, Calkins) have shown that the dependence of depression on external factors is very great. If under normal conditions depression occurs in the infusorian Paramecium aurelia every 40–50 divisions, then by changing the cultivation conditions it is possible to induce depression already after 5–6 divisions or, conversely, to postpone its onset up to the 170th division; in other words, it is possible to shorten the periods between two depressions by 10 times or lengthen them by 3 times. Nevertheless, mild depressions, expressed only in an insignificant decrease in the life rhythm, are observed as a rule and without any visible causes, even under the best cultivation conditions, wherein their regulation does not require the mandatory onset of conjugation, which can be replaced by the process of endomixis associated with the complete reconstruction of the nuclear apparatus. The phenomenon of depression is thus connected with the questions of the aging of organisms, their rejuvenation, with the theory of the sexual process, and with the problem of immortality.