The Protection of Health 607 



and kept at a definite low temperature in a refrigerator. This 

 is done to allow the poison to " season " or mature. At first 

 it deteriorates rapidly, but is finally found, by tests which are 

 made at intervals of a month, to be relatively constant or stable. 

 It is then possible to determine the amount of the dose. This 

 is the diphtheria toxin. 



Horses to be used in preparing the antitoxin for diphtheria 

 must be absolutely sound. The antitoxin stable, scrupulously 

 sanitary in all its appointments and conditions, never receives 

 an animal which does not meet satisfactorily every known test. 

 The selected horses are inoculated with the diphtheria toxin 

 the dose of which, beginning with a very small fraction of a 

 cubic centimeter, is gradually increased to the maximum, per- 

 haps 600 cubic centimeters. Inoculations are made at intervals 

 of three to five days, the frequency together with the amount 

 of serum to be injected being determined by the reaction of 

 the animal to previous injections, as shown in fever, and by its 

 complete recovery. If injections can be given at short intervals, 

 the resulting antitoxin serum will have the greatest potency. 

 The treatment is continued usually for a period of from forty 

 to sixty days. When antitoxin is produced freely, as after 

 twenty-eight to thirty days, just as much blood is drawn from 

 the jugular vein of the animal as it can spare without injury. 



The blood serum is stored for two days or more in tall glass 

 cylinders, to allow the blood to coagulate. The clotted blood 

 is then removed, leaving a clear, amber-like fluid, which is the 

 diphtheria antitoxin serum. This is treated with a preserva- 

 tive, filtered, examined, and tested for potency, purity, and 

 safety. It is stored in small containers for distribution and use. 

 After the product is safely packed, samples are taken at random 

 and examined independently by experts for possible contam- 

 ination. Only after this final examination and approval is 

 the product distributed. 



When a serum is placed on the market samples are purchased 

 and tested by Federal experts. If Federal examination reveals 



