DIPHTHERIA. 4 1 1 



The animal chosen should be free from tuberculosis 

 and glanders, as tested by tuberculin and mallein, but 

 need not be expensive. A horse with a disabled foot 

 will answer well. Rheumatic horses should be rejected. 

 In the beginning a small dose of the toxin — about -^ 

 ccin. — should be given hypodermically to detect indi- 

 vidual susceptibility. Horses vary much in this particu- 

 lar, as Roux has pointed out. I have found light-colored 

 horses to be distinctly more susceptible than dark-colored 

 ones, a fact which has some substantiation in the clinical 

 observation that blonde children suffer more severely from 

 diphtheria than dark-complexioned ones. 



If well borne, the preliminary injection is followed in 

 about six days by a larger dose, in six days more by a 

 still larger one, and the increase is continued every six 

 days or so, according to the condition of the animal, until 

 enormous quantities — 500 or even 1000 c.cm. — are 

 introduced at a time. 



As the expression of quantity alone is very misleading, 

 and to know exactly what toxin-strength the horse is 

 receiving, I use a special term, factor, by which to 

 express it. Instead of stating that the animal received 

 10, 50, or 100 c.cm. of toxin, I record that it receives 

 10, 50, or 100 factors, the term factor being used to 

 express 100 times the least certainly fatal dose of toxin 

 per 100 grams of guinea-pig. The number of factors 

 in a given quantity of toxin naturally varies with its 

 strength, and it will at once be seen that it is advanta- 

 geous to express the strength regardless of the quantity. 



The toxin causes some local reaction — at first a dis- 

 tinct inflammation, later a painful edema and a febrile 

 reaction. The amount of local irritation is much less 

 marked when the injections are made slowly ; and a 

 gravity apparatus, which is filled with the amount of 

 serum to be injected, suspeuded from the ceiling of the 

 stable so that the toxin is allowed to take its own time to 

 enter the tissues, can be recommended (Fig. 87). Sometimes 

 it takes several hours to inject 500 c.cm. in this manner. 



