TETANUS 327 



In the preparation <>i' Ilie antitoxin, it is necessarj^ to 

 force a susceptible animal, like the horse, to produce in its 

 blood a quantity of the protective substances, so that the 

 blood can be drawn and the serum obtained. In producing 

 the serum, the animal is hyper-immunized by the addition 

 of repeated doses of the toxin or poison produced by the 

 organism, beginning with very minute doses and gradually 

 increasing them. This treatment with constantly increasing 

 doses of the toxin is continued until the body of the horse 

 has produced a large quantity of the substanee that will 

 neutralize the toxin. Fortunately, the body can produce 

 an amount of the protective substances in excess of that 

 which is necessary to render harmless the toxin introduced. 



If some of the blood of the hyper-immunized animal is 

 carried to an animal that is just beginning to show symp- 

 toms of tetanus, the antitoxin will he ready to neutralize the 

 poison as it is formed by the growth of the organisms. It 

 will tide the body of the diseased animal over the period of 

 danger, and give it time to protect itself by the manufac- 

 ture of its own antitoxin. 



The transfer of the protective substances is accomplished 

 by drawing a small portion of the blood, allowing it to 

 clot, and using the clear serum, which formerly represented 

 the commercial product. Ways have now been found by 

 which the protective substances can be concentrated by 

 chemical means, a distinct advantage, since it avoids the 

 introduction of large quantities of liquid into the animal 

 to be protected. 



The protective serum is expensive, and hence is used 

 only on valuable animals. Its widest use is in the preven- 

 tion of the disease in man. The immunity thus produced 

 is passive and persists for only a short time. 



