142 DIPHTHERIA AND PSEUDODIPHTHERIA. 



mals, produces all the symptoms of true diphtheria, was 

 soon followed by the discovery of Behring, which showed that 

 the blood-serum of animals injected with the bacilli of diph- 

 theria contains a substance which when inoculated into sus- 

 ceptible animals is able to immunize them from lethal doses 

 of the bacilli. 



These substances, called antitoxins, are obtained from ani- 

 mals having little or no susceptibility to the disease, and 

 they have been used extensively both in the prevention and 

 cure of diphtheria since 1894. 



These antitoxins as exhibited therapeutically are obtained 

 from the blood-serum of horses, as first suggested by Roux, 

 and are prepared as follows : 



Immunization. A good-sized horse, which has been demon- 

 strated to befree from tuberculosis and glanders, by the injecting 

 of tuberculin and mallein, and free from all rheumatic and chronic 

 disease, is gradually immunized to the diphtheritic poison by 

 being injected with very small doses of the virulent toxins 

 from a diphtheria bouillon culture filtrated through porcelain. 

 The initial dose consists of 0.10 c.c. mixed with an equal 

 quantity of Gram's iodine solution ; this should produce 

 little or no constitutional disturbance, and very little if any 

 local effect. Four or five days after this first injection a 

 second injection, consisting of pure toxin 0.10 c.c., is used, 

 and every four or five days thereafter injections are re- 

 peated in progressively larger doses until the animal is 

 able to withstand doses of from 400 to 500 c.c. of toxin. 

 During those injections the animal may show decided local 

 effects, such as swelling and osdema at the point of inocula- 

 tion, but no very marked constitutional disturbances. During 

 the progress of this immunization, at intervals, by punctur- 

 ing of the jugular vein with a sterilized trocar, some blood 

 is withdrawn from the animal and its serum tested as to its 

 antitoxic value, and when the same is found sufficient the 

 toxin injections are repeated at longer intervals to maintain 

 the antitoxic property of the animal's serum, and the next 

 process is begun. 



Standardization. A large quantity of blood, 4 or 5 liters, 



