232 DISEASES FROM HARMFUL ORGANISMS 



61) is the best-known example, which do not penetrate 

 into the body and become distributed through it, but lo- 

 cate in some particular region, in the case of diphtheria, 

 the region being the mucous lining of the throat. The 

 organisms grow there and multiply actively and pour out 

 their poisons. These are absorbed into the body, distri- 

 buted through it by the circulation, and poison the 

 individual cells. The poison, which is known as the 

 toxin of the disease, stimulates the cells to produce the 

 anti-bodies which in this case constitute a7iti-toxin. 



Fig. 61. —The Bacteria That Cause Diphtheria. 



Whether the patient survives or succumbs depends on 

 whether the anti-toxin is or is not produced in suflBcient 

 quantities to neutralize the toxin. 



Artificial Anti-toxin. — It is possible to grow 

 diphtheria organisms in test tubes in a suitable culture 

 medium, and thereby produce large quantities of toxin. 

 This toxin is then injected into healthy horses in quan- 

 tities not sufficient to poison them seriously, but ade- 

 quate to stimulate their cells to the production of anti- 

 toxin. After a suitable interval has elapsed, during 

 which the cells of the horses' bodies are manufacturing 

 anti-toxin, blood, which will of course contain it, is with- 

 drawn, the corpuscles removed, and the clear liquid put 

 up in suitable form for introduction into the bodies of 

 diphtheria patients. Thus the poison which is being 



