18 THEORIES OF IMMUNITY 



logic state is brought about. The symptoms and the ana- 

 tomical lesions of disease were recognized but it was not known 

 how these symptoms and lesions were produced. It was 

 learned how to ." accustom" the organism to certain poisons, 

 to "vaccinate" against certain diseases and to effect cure by 

 certain antidotes. But we have been obliged to recognize 

 that methods, either preventive or curative, applied with 

 success in certain cases, do not give any appreciable result 

 in others. 



Thus neither the mechanism of the pathogenicity nor that 

 of the pathologic state nor that of the cure was understood, 

 so that curative measures were necessarily limited to attempts 

 to relieve symptoms and to the treatment of lesions by means 

 found by chance experiments. 



~~In order to throw light on the mechanism of cure, especially 

 in the infectious diseases, Metchnikoff put forth his phago- 

 cytic theory, according to which, the leukocytes, the only 

 cells of the organism provided with a membrane which could 

 engulf microbes, digested these microbes and thus destroyed 

 the primary cause of the disease. 



However, much before the phagocytic theory, vaccina- 

 tion of the organism against smallpox, anthrax, erysipelas, 

 chicken cholera, carbuncle, had been successful. The first 

 practical results in the curative treatment of an infectious 

 disease, viz., the cure of diphtheria by antitoxic serum, did 

 not result from the conception of immunization by leukocytes. 



Vaccination by soluble bacterial secretions had been 

 observed in numerous diseases, as for example : by Chauveau 

 in lambs born of ewes inoculated with anthrax during ges- 

 tation; by Salmon and Smith in their experiments in hog 

 cholera; by Charrin in pyocyaneous infection and by Roux 

 and Chamberland in symptomatic anthrax and the infection 

 by septic vibrio. Moreover the production of an antitoxin 

 "in excess" for diphtheria and tetanus following injection 

 of toxins filtered from both living and dead organisms was 

 demonstrated; as well as the fact that these bacterial poisons 

 might be fixed to and might act not only on the leukocytes 

 but also on every other celL 



These observations inspired Ehrlich to a more general 



