88o PHAGOCYTES AND PHAGOCYTOSIS IN IMMUNITY 



garding the number of bacteria that may be injected without harm. Wright noted 

 that the effect produced by the same dose, e.g., 1,000,000 gonococci, upon different 

 individuals varied greatly according to whether they were well, moderately severely 

 infected, or severely infected. The general knowledge gained by experience concerning 

 the relative toxicity of different bacterial antigens may be considered as of some im- 

 portance — but it is still more important that one determine the relative sensitivity 

 of the infected individual. This can be done by the intradermal injection of the heat- 

 killed antigen. 



The writer has found that the heat-killed saline suspension of bacteria should not 

 contain an excessive number of bacteria; when a too dense suspension is injected in- 

 tradermally into a very sensitive individual, even in as small a volume as 0.5 minim, 

 this may be followed by local suppuration and necrosis. A rough-and-ready method 

 is to prepare the suspension in a test tube with a diameter of 15 mm. and of such a 

 density that the inoculating needle can be seen plainly through the suspension. One 

 (or i| minims) of such an antigen is injected intradermally. According to the reac- 

 tion obtained a dose of 0.5 minim or less is injected subcutaneously. The injections are 

 given daily and the dose increased or not by 0.5 minim according to the local reaction 

 produced and according to the rapidity with which the local reaction subsides. In 

 very sensitive individuals it may be necessary to keep to a minute dose for many days; 

 then when the preliminary sensitivity disappears the dose can be increased, and about 

 this time the site of infection shows signs of healing. 



We have probably overestimated the amount of antigen necessary to give pro- 

 tection and aid in overcoming infection. Cooper' found that i minim of heat-killed 

 type I pneumococcus suspension injected daily into the submucosa of rabbits for ten 

 days rendered them immune for months. 



Recent studies on local tissue immunity, and on the use of detoxicated antigens 

 promise further advances for prophylactic and therapeutic immunization. 



' Cooper, M. L.: /. Infect. Dis., 38, 491. 1926. 



