BACTERICIDAL OB ANTI-BACTERIAL IMMUNITY. 



193 



Finally, it is worthy of note that it has been possible, by the adapta- 

 tion of a fresh animal of the appropriate species to these precipitating 

 sera, to obtain "antibodies"; in the case of milk adaptation, for exam- 

 ple, by the use of the so-called lacto-serum, to secure an an til acto- serum 

 capable when added to the test fluids of preventing the formation of the 

 specific precipitate. 



A great deal of most careful research has been devoted to the nature 

 of the precipitating substances which the scope of this book does not 

 permit us to touch upon. But it should be said that in their resistance 

 to heat and in other ways the precipitating substances appear to be more 

 closely related to agglutinating than to lytic Substances. 1 



Although we have considered separately the development in the body 

 of cytolytic, agglutinating, and precipitating substances, it should be 

 remembered that these may be formed together in the same animal. 



The effects of foreign cells and their derivatives upon whatever body 

 cells produce the lytic, agglutinating, and precipitating substances are 

 apparently not lasting, since if the injections be suspended they gradually 

 disappear from the serum. The time of their disappearance, however, 

 like that of appearance, is not regularly the same, even in the same 

 animal. 



The Bearing of the New Studies on Serum. Therapy. We have seen in an 

 earlier section that the use of the blood-serum of animals immunized against pathogenic 

 micro-organisms for protective purposes in man lias been of practical value in but few 

 instances, and these mainly in cases in which the protective action was antitoxic. Pro- 

 tective sera for pneumonia and typhoid, streptococcus septicaemia, plague, tuberculo- 

 sis, cholera, and many other infectious diseases have been persistently tested and found 

 to be for the most part of doubtful value in man. 



But in the light of the new knowledge of cytolytic sera, and the conditions under 



TABLE (AFTER ASCHOFF) SHOWING VARIOUS FORMS OF ADAPI 

 RELATIONSHIPS AND SYNONYMS. 



PRODUCTS, WITH THEIR 



L3 



