BACTERIOLOGICAL TOXINS AND ANTITOXINS 117 



cause a marked decrease in the mortality from diphtheria in those 

 communities in which it had been used. Since then thousands 

 of lives have been saved by its means. Records show that when 

 antitoxin is used on the first day of the disease practically no mor- 

 tality occurs. 



Production of Antitoxin for Therapeutic Purposes. Toxin 

 is first prepared by cultivating a virulent strain of the bacilli in 

 a suitable broth medium for ten days or two weeks. The culture 

 is then passed through a porcelain filter which retains the bacilli 

 and allows the strong toxin solution to pass through. The potency 

 of this toxin is estimated by injecting carefully measured doses 

 into a series of guinea pigs. Usually about -^ro c.c. of a moderately 

 strong toxin is fatal. The smallest amount of toxin that will 

 kill in four days a guinea pig weighing 250 grams is spoken of as 

 the toxin unit or minimum lethal dose. This preliminary titration 

 serves to indicate how much toxin can with safety be injected into 

 a horse of much heavier body weight. 



Horses are chosen for the production of commercial antitoxin 

 partly because large quantities of serum can be obtained from each 

 animal and partly because the serum is normally of a bland nature. 

 Strong healthy horses which have been proved to be free from 

 tuberculosis and glanders are injected with gradually increasing 

 doses of the toxin ; the first doses are usually guarded by an injec- 

 tion of antitoxin given at the same time. As soon as the reaction 

 passes and the temperature becomes normal a slightly larger dose of 

 toxin is given, until by the end of about eight weeks the horse can 

 tolerate many times the amount received on the first day. Injec- 

 tions are continued and weekly tests are made of the serum until 

 it is found that the amount of antitoxin no longer increases. At the 

 end of from four to six months the serum may contain from 700 

 to 1000 units of antitoxin per cubic centimeter. When no further 

 increase appears the horse is bled aseptically from the jugular 

 vein and the blood stored in the refrigerator for two days in order 

 that the serum may separate from the clot. At the end of this 

 period the serum is siphoned off, and after the addition of a small 

 amount of an antiseptic as a preservative it is ready for use. A 



