130 PHARMACEUTICAL BACTERIOLOGY. 



blood is drawn off into sterilized liter tubes, which are plugged with cotton. 

 From nine to twelve liter of blood are taken from the horse at one time and 

 the bleeding is repeated four or five times at intervals of about six months. 

 The punctured wound is closed by keeping an artery forceps in position for 

 a short time. 



E. Securing the Serum. The blood tubes are set aside until the clot has 

 formed and settled to the bottom. The clear serum is siphoned off into a 

 large flask, 0.25 per cent, of trikresol is added as a preservative and to kill 



FlG. 57. Bleeding the horse after a maximum amount of the antitoxin of diphtheria has 

 been developed in the blood. The animals pay but little attention to the operation. 



any germs that might be accidentally present, and then filtered through 

 several thicknesses of filter paper, under pressure (suction). The perfectly 

 clear, sterile and germ-free serum constitutes the antitoxin of diphtheria and 

 is ready for use as soon as it is standardized and put into suitable containers. 

 F. Standardizing the Antitoxin of Diphtheria. Since the antitoxic valence 

 of horse serum as above described varies somewhat, it is necessary to deter- 

 mine the quantitative value in order that physicians may know what amounts 

 to administer in the treatment of diphtheria. The standard unit of strength 



