Loop

LOOP (in bacteriological practice), a platinum wire sealed into a glass rod (or fitted into a special holder) and bent at the free end into the shape of a ring (circle). The so-called normal loop (Pfeiffer) has a diameter of approximately 2 mm. The loop is used for capturing bacteriological material (cultures on solid and liquid media, secretions, etc.) and for inoculating it; the material taken with the loop is introduced into a liquid nutrient medium or spread on the surface of a solid one. A "normal" loop is one that captures a specific weight amount—2 mg of bacterial mass from a solid nutrient medium. The loop is calibrated such that the bacterial mass it captures is placed on a slide; this mass is then weighed on chemical scales. The procedure is repeated several times; the average of all determinations characterizes the given loop. When injecting material into an animal with a loop, a specific weight amount of bacterial mass (2 mg) is introduced. To go from 1 loop to 1/2, 1/4, etc. loops, one loop is emulsified in physiological solution and then 1/4, etc. of the emulsion is injected.