PHAGOCYTOSIS 33 



the number of bacteria contained in such leucocytes 

 counted. The contents of about eighty to one hundred 

 cells are usually counted, and an average is taken. 

 The average number of bacteria in such leucocytes is 

 spoken of as the " jDhagocytic index." The phago- 

 cytic index of the tested serum divided by that of the 

 normal control serum gives the '^ opsonic index." 



I mention this test in detail, as it is one which can 

 come within the reach of all practitioners, as practic- 

 ally the only requirements for performing the test are 

 a small incubator, a microscope, and some bacterial 

 cultures. 



In applying vaccines in the treatment of disease, 

 the opsonic test affords us an extremely useful guide 

 as to the time the vaccine injections should be given, 

 and as to the progress that has been made by the 

 employment of vaccine. 



Immediately after the injection of a vaccine there 

 is a brief period during which the opsonic power of 

 the patient is depressed below its original state. This 

 is called the negative phase. The length of time 

 occupied by the negative phase depends both upon 

 the condition of the patient and upon the size of the 

 dose given. After this, there is a gradual rise in the 

 opsonic power, at first rapid, later slower, until a 

 maximum is reached after a varying number of days. 

 This period of rise represents the positive phase. 

 The second inoculation of vaccine should, therefore, 

 be made when the opsonic power is beginning to sink 

 after the highest point of the positive phase. Should 



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