198 INFECTION AND IMMUNITY 



The diphtheria antitoxin which is now extensively 

 and successfully used in the specific treatment of the 

 disease may also be used to prevent its development 

 in persons exposed to infection. From five to ten 

 cubic centimetres of a reliable antitoxin is used for 

 this purpose. This is injected subcutaneously and 

 is a harmless procedure which has been proved to 

 be efficacious in most cases, or at least to greatly 

 modify the severity if an attack occurs. Where child- 

 ren have been exposed to infection, or under cir- 

 cumstances which prevent the proper isolation of a 

 diphtheria patient, it is prudent to resort to such 

 preventive inoculations. As is generally known, the 

 antitoxin is usually obtained for practical purposes 

 from horses which have been rendered immune by 

 repeated and gradually increasing doses of diphtheria 

 toxin that is, the poisonous substance developed by 

 the diphtheria bacillus during its growth in suitable 

 culture media. The antitoxin is contained in the 

 blood of the immune animal, and the clear blood 

 serum which separates on standing, from the "clot," 

 which contains the red and white blood corpuscles, is 

 spoken of as " antitoxin " and is used in the treat- 

 ment and prevention of the disease. From this blood 

 serum a more concentrated antitoxin may be obtained 

 by chemical methods, but this has not come into 

 practical use. 



