CHAPTER XXV. 



IMMUNITY AND VACCINE THERAPY. 



General consideration.* It has long been recognized 

 that certain species of animals do not suffer from certain 

 infectious diseases. It has also been noticed that when animals 

 or man recovered from certain infections that they did not 

 readily contract that disease again. This resistance to the 

 invasion of certain microorganisms has been termed immunity. 

 It is, however, relative, for in many instances it can be over- 

 come either b^ excessive infection or by changing the physical 

 condition of the host. The resistance or immunity found to 

 exist against infection is divided into two quite distinct classes 

 (1) natural, i. e. where the individuals of a species do not 

 contract the disease and (2) acquired, i. e. where they become 

 resistant to a specific infection after having recovered from 

 one attack. 



* For the further study of the facts and principles concerning 

 the production of immunity and immune bodies the student is re- 

 ferred to the following works on this subject: 



Citron. Immunity, methods of diagnosis and therapy and their 

 practical application, 1912. 



Ernst. Modern Theories of Bacterial Immunity. Boston, 1903. 



Kraus and Levaditi. Handbuch der Technik und Methodik der 

 Immunitatsforschung, 1909. 



Metchnikoff. Immunity in Infective Diseases. Cambridge, 1905. 



Much. Die Immunitatswissenschaft, 1911. 



Miiller. Vorlesungen uber Infektion und Immunitat, 1910. 



Nuttall. Blood Immunity and Blood Relationship. Cambridge, 

 1904. 



Sternberg. Immunity, Protective Inoculations in Infectious Dis- 

 eases and Serum-Therapy. New York, 1895. 



Sobernheim. Zeit. f. Hyg., Bd. XXV (1897) p. 301. 



Vaughan and Novy. Cellular Toxins or the Chemical Factors in 

 the Causation of Disease. 



Wassermann. Immune Sera, Haemolysins, Cytotoxins, and 

 Precipitins. New York, 1904. 



