PATHOGENIC BACTERIA 1 29 



Preparation of Toxin. The bacillus is grown in muscle- 

 sugar-free bouillon with an alkaline reaction. Acids prevent 

 toxin formation. There should be a free supply of oxygen, 

 and, therefore, large shallow flasks are used. The maximum 

 toxicity is developed in seven to ten days. The strength should 

 be -5-^-5- c.c., fatal for 5oo-gram guinea-pig. 



Preparation of Antitoxic Serum. Horses are rendered 

 immune by gradually increased doses of diphtheria toxin, the 

 power of the toxin having first been standardized by its neu- 

 tralization with some standard antitoxin in powdered form. 

 The toxin is at first injected subcutaneously, then intravenously, 

 and after several months' treatment a resistance is obtained 

 that will withstand 300 to 500 times the original lethal dose. 

 The horse is then bled, and from five to nine liters withdrawn, 

 this is then allowed to coagulate, and under very careful 

 precautions the serum is placed in sterile packages, its strength 

 having first been compared with a standard furnished by the 

 United States Government. 



Antitoxic Unit. A normal antitoxic serum is one that 

 contains in each cubic centimeter one immunity unit. An 

 immunity unit, according to Ehrlich, is the amount of antitoxic 

 serum which will neutralize 100 times the nr'nimum lethal 

 dose of toxin, when serum and toxin mixed and injected into 

 a 25o-gram guinea-pig does not cause death in four days. Thus, 

 if the serum will protect in doses of -^ c.c., then each cubic cen- 

 timeter has 50 units power, and 20 c.c. will contain 1000 units, 

 or will be sufficient to neutralize an amount of toxin that would 

 be fatal for 25,000 kilos (12,500 pounds) of guinea-pigs, or 

 100,000 pigs weighing 250 grams each. 



Streptococcus in Diphtheria. Streptococci have been 

 found quite constant in diphtheria, but they resemble the 

 Streptococcus pyogenes, and have no specific action. 



Bacillus of Typhoid or Enteric Fever (Eberth-Gaffky) . 

 Origin. Eberth found this bacillus in the spleen and lymphatic 

 glands in the year 1880, and Gaffky isolated and cultivated 

 the same four years later. 



Form. Rods with rounded ends about three times as long as 



