HISTORIC DEVELOPMENT OF IMMUNOLOGY 33 



THEORIES UPON WHICH IMMUNE THERAPY 

 IS FOUNDED 



The methods of vaccination introduced by 

 Jenner and Pasteur were based on the observa- 

 tion that survival after a modified form of a 

 disease resulted in protection, but they did not 

 analyze thoroughly the nature of this protec- 

 tion. The further application of immune meth- 

 ods has been the result of innumerable investi- 

 gations into the mechanism of immunity, some 

 of which may be briefly mentioned. 



Phagocytosis In 1884 Metchnikoff published 

 the first of a series of observations upon the be- 

 havior of certain cells of the lower animals 

 toward insoluble particles that may be present 

 in the tissues of these animals. The outcome of 

 these investigations was the establishment of 

 his well-known doctrine of phagocytosis; the 

 principle of which is that the wandering cells 

 of the animal organism, the leukocytes, possess 

 the property of taking up and rendering inert 

 and digesting microorganisms which they may 

 encounter in the disease. Metchnikoff believes 

 that in this way immunity from infection may 

 in many cases be explained. He believed that 

 immunity was essentially a matter between the 



