300 PATHOGENIC BACTERIA. 



being large enough to furnish a considerable quantity 

 of serum, recommends itself strongly for the purpose. 



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 i 

 c.cm. should be given hypodermically to detect indi- 

 vidual susceptibility. Horses vary much in this particu- 

 lar, as Roux has pointed out. The author 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 500-1,000 c.cm. are intro- 

 duced at a time. 



As the expression of quantity alone is very misleading, 

 and to know exactly what strength the horse is receiving, 

 the author has devised a special nomenclature by which 

 to express it. Instead of stating that the animal received 

 10, 50, or loo c.cm. of toxin, we now say it receives 10, 

 50, or loo factors, the term factor being used to express 

 loo times the least certainly fatal dose of toxin per 100 

 grams of guinea-pig. The number of factors in a given 

 quantity of antitoxin naturally varies with its strength, 

 and it will at once be seen that it is advantageous to ex- 

 press strength regardless of 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 

 scrum to be injected, suspended from the ceiling of the 



