506 



IMMUNITY 



compound called 606, which gave immunity to the mice. Ehrlich 

 tried his 606 on a certain disease in human beings caused by spi- 



antibodies "Ioclc\xf> 

 toxins on cr 



Diagrammatic representation of toxins uniting with antitoxins. The toxin has stimulated the 

 cell to develop an antitoxin which locks or neutralizes the toxin. This is according to the side- 

 chain theory of Paul Ehrlich. 



rochaetes and found that it cured them, also. He called the arsenic 

 compound salvarsan. He thought the salvarsan united with the 

 cells of the body and helped to produce an immunity. Instead, it was 

 later proved that the dye united with the spirochaete and killed it. 



Ehrlich was the founder of the humoral or side-chain theory of 

 immunity, which is still generally accepted by biologists of to-day. 

 The humoral theory states that protective substances are produced 

 within the body, usually in the blood, which counteract the effects 

 of bacteria. Metchnikoff and Ehrlich stimulated research in the 

 study of immunity. Since then there has been much progress. 

 To-day, it is one of the big features in preventive treatment. 

 Many of the cures and discoveries of to-morrow will be built on 

 the foundations laid by these men. 



Types of immunity. Natural immunity is the immunity one has 

 at birth. It stays with the individual always and, therefore, there 



