IMMUNITY AND HYPERSUSCEPTIBILITY 223 



tuberculosis by Webb. In most diseases these methods are re- 

 garded as too dangerous for extensive use. 



Living virus, altered in its virulence, was first used by Edward 

 Jenner, when he inoculated with cow-pox (vaccinia) and induced 

 immunity to small-pox. Cow-pox is doubtless due to the organism 

 which causes small-pox, attenuated by its life in the body of the cow. 

 Viruses artificially cultivable are attenuated by a variety of pro- 

 cedures, and are employed to induce immunity. Pasteur's vaccine 

 for anthrax, for chicken cholera and possibly the treatment of 

 rabies with dried spinal cord, are examples of the application of 

 this principle. Virus of extraordinary virulence is sometimes in- 

 jected after previous treatment with attenuated organisms, in 

 order to confer a higher degree of immunity. Thus Pasteur 

 employed the most virulent rabies virus obtainable, virus fixe, in 

 the immunization against rabies. 



Living virus, of full virulence, but apparently influenced in some 

 way by the body fluid containing it, is employed in immunizing 

 against rinderpest and against Texas fever. The bile of an animal 

 dying of rinderpest is injected subcutaneously in doses of 10 c.c. 

 into cattle. Kolle has shown that the virus can be separated from 

 such bile in fully virulent condition; so it appears that some con- 

 stituents of the bile restrain the activity of the virus. In Texas 

 fever, blood of young animals containing relatively few of the 

 parisites is used to inject new animals. 



Immunization by injection of dead microbic substance is now 

 extensively employed in the prophylaxis of cholera, typhoid fever 

 and plague. As a result of such injections there is a marked in- 

 crease in specific agglutinins and bacteriolysins in the blood. The 

 principle of general immunization is also employed with some suc- 

 cess in the treatment of subacute, chronic or recurrent local 

 infections, the production of antibodies and their circulation in 

 the blood and lymph exerting a favorable effect upon the local 

 lesions. The emulsions of dead bacteria employed are called 

 bacterial vaccines. 



The soluble products of bacterial growth are injected into 



