IMMUNOLOGY. IMMUNITY AND IMMUNIZING AGENTS 241 



made intelligible by decimal figures representing the number of bacteria 

 which _the average phagocyte will take up. We may assume that one 

 phagocyte in normal blood will ingest an average of 10 bacteria, repre- 

 sented in the index by the figures i.o, but in disease (chronic) the phago- 

 cytes may only take up an average of 3, 6, or other numbers, represented 

 by the figures 0.3, 0.6, etc. After stimulation the phagocytes may take 



FIG. 59. Opsonic Incubator. The determination of the Opsonic Index has become 

 so important that these incubators have been made to meet the demands for an appa- 

 ratus in which twenty pipettes can be incubated at one time and so that any tube may 

 be examined during the progress of the experiment without changing the temperature of 

 the others. There are twenty tubes for opsonic pipettes and an extra tube. The tubes 

 may be easily removed when derired by means of a key which accompanies the incubator. 

 On top there are eight tubes, 22 mm. in diameter, for test-tubes. Each is provided with 

 a nickel-plated cap. The incubator is supplied with thermometer, thermo-regulator, 

 and a two-flame burner, with wire guard. 



up 15, 25, or even numbers of bacteria represented in the index by the 

 figures 1.5, 2.5, etc. 



Taking the opsonic index of an individual's blood cells for considerable 

 delicate technic. In brief, it is performed by mixing together equal vol- 

 ume quantities (measured in a capillary tube) of blood serum and an emul- 

 sion of bacteria and incubating for 1 5 minutes at 37.5 C. Then making a 

 thin smear of the mixture on a microscope slide, drying and staining, and 

 counting the number of bacteria enclosed in each white blood-corpuscle 

 (50 to 200 cells counted) and striking an average. This average is the 



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