454 PRINCIPLES OF VETERINARY SURGERY 



impossible the contraction of the muscles they supply,, and 

 destruction of the medullary centers renders impossible the 

 contraction in the corresponding region. Chloroform con- 

 siderably diminishes the contractions, or makes them disap- 

 pear entirely. When the motor nerve of a muscle is intact, 

 it can no longer undergo contraction from the influence of 

 tetanic toxin, if not supplied with sensitive fibers. 



The study of the comparative excitability of the different 

 parts of the nervous system elucidates the mode of action of 

 the toxin. The tetanic poison does not modify the excitabil- 

 ity of the motor nerves ; but acts as if it was concerned with 

 the sensitive system. It acts on other nerve centers, arriv- 

 ing at them by way of the nerves, after more or less time. 

 The symptoms of tetanus vary according to the point of in- 

 oculation and the part of the nerve centers first attacked. It 

 seems that the nerve fibres act as conductors of the toxin. 

 Thus, M. Binot has shown that it is possible to produce vari- 

 eties of tetanus in the cavy, according to the point of inocu- 

 lation. Subcutaneous or intramuscular inoculation gives 

 generalized motor tetanus. Inoculation in the testicle or' 

 uterus gives visceral tetanus with a long period of incubation 

 and without spasms. The cavy, thus inoculated, quivers at 

 the least touch, walks upon the tips of its toes as if O'U 

 needles, and dies usually from asphyxia. The toxin was con- 

 ducted by the sympathetic nerves. By inoculating under the 

 skin, but in a tuberculous gland innervated by the sympa- 

 thetic system, there will be visceral tetanus but no con- 

 tractions. 



The nerve fibers therefore conduct the toxin. It does not 

 attack the nerve centers through the circulation, as it does 

 not kill by the intravenous inoculation of a dose seven times 

 larger than a fatal subcutaneous dose. This fact is demon- 

 strated by the following experiment: — Two rabbits are each 

 inoculated in the sciatic nerve with a fatal dose of the toxin; 



