446 PRINCIPI-ES OF VETERtNARY SURGERY 



in a sufficient temperature : in summer at a temperature of 

 28° to 31° C. the frog is easily rendered tetanic; in winter at 

 5" to 8° C. the frog- is refractory, and in order to produce the 

 disease the temperature must be artificially raised to 30° to 

 39° C. The order of sensibility to tetanus toxin is as follows, 

 if we base our conclusions on the dose which kills a gram of 

 animal weight. By starting with the dose that kills one 

 gram of horse : To kill a gram of cavy requires twice as 

 much ; of dog four times as much ; of mouse twelve times as 

 much ; of rabbit two thousand times as much ; and of hen two 

 hundred thousand times as much. 



Mode of Action of Tetanus Toxin. — The writers who 

 first devoted themselves to the study of the poisons of Nico- 

 laier's bacillus thought that these soluble products acted di- 

 rectly upon the organism like other well known toxins or 

 alkaloids, e. g. strychnia. Tetanus toxin, although exactly 

 similar to diphtheric toxin in its essential properties, differs 

 from it in its action on animals. Diphtheria toxin has both 

 immediate and remote effects, while tetanus toxin never 

 acts immediately. An uncertain period of time (several 

 hours or several days) always elapses between the injection 

 of the toxin and the appearance of the first tetanic symptom. 

 It is a real period of incubation during which there is no 

 noticeable disturbance to the health. This incubation has 

 been observed since the first studies on the subject, even by 

 Knud Faber. Courmont and Doyon have shown that this 

 period of incubation is constant in all animals, whatever may 

 be the dose or the channel of entrance. The dose has but a 

 slight influence on the duration of the period of incubation, 

 which varies with the different aniriials. From the subcutan- 

 eous injection of an average dose it is of eight hours duration 

 in the white mouse, thirteen to eighteen hours in the cavy, 

 eighteen to thirty-six hours in the rabbit, thirty-six to forty 

 hours in the dog, four days in man, four to nine days in the 



