PRINCIPLES OF VETERINARY SURGERY 445 



desiccated, but the toxins are not pure and may be heated to 

 loo° without alteration. Tannin and magnesia sulphate also 

 precipitate them. With the latter the precipitate rises to the 

 surface and can be easily skimmed. Successive precipita- 

 tions bring out all of the toxins. The dry precipitates keep 

 for an indefinite period, and their activity is formidable. 



The bacillus of tetanus elaborates a diastatic substance in 

 the cultures that acts much like digestive ferments. It lique- 

 fies gelatin. It is perhaps mixed with tetanic toxins, as the 

 cultures attenuated by heat, light and air, lose not only their 

 toxicity but also their property of liquefying gelatin. 



EXPERIMENTAL STUDY OF TETANUS TOXIN. 

 — The toxin, when injected into the body of an animal, pro- 

 duces symptoms identical with those of spontaneous tetanus. 

 The sensibility of animals to tetanus toxin is parallel to their 

 receptivity to the complete culture. In order of a decreasing 

 sensibility we may successively enumerate man, white 

 mouse, cavy, rabbit, solipeds, dog, pigeon and the hen. 



1-1,000,000 cc will kill a mouse 



i-io,ooocc will kill a cavy 



1-4 cc will kill a rabbit 



1-2 cc will kill a frog 



2 cc will- kill a horse 



4 cc will kill a dog 



10 cc will kill a hen. 

 The hen is not naturally immune, as was once su])posed. 

 Courmont and Doyon have shown that fatal tetanus may be 

 easily produced in this animal with moderate doses. The 

 pigeon is more sensitive than the hen to tetanic toxin. The 

 frog has been used in the laboratories since the researches 

 of Courmont. Metchnikoff has demonstrated that the tor- 

 toise, the alligator and the scorpion are refractory to tetanus 

 and will resist even large doses of the toxin, either hot or 

 cold. In order to give tetanus to a frog it is necessary to work 



