CHANNELS OF INTKCTION 1 33 



fertilizers, hides, hair or wool from infected countries. When 

 the extent of this traffic is realized, it is easy to understand 

 how anthrax has been brought to this country and why it 

 occasionally appears here and there over a large part of the 

 continent. Many outbreaks, as well as isolated cases, illustrat- 

 ing this common method of dissemination are on record. 



The period of incubation \s VQ.xy sXxoxi. In inoculated ani- 

 mals it ranges from i to 5 days. 



§ 120. Animals attacked. Nearly all species of ani- 

 mals suffer from anthrax. The herbivora and rodents are 

 most susceptible. Horses and mules often suffer from it. 

 M'Fadyean has reported outbreaks aggregating 54 cases, of 

 which 49 were cattle, 4 horses and i pig. He states also that 

 for a period of 5 years there had been reported 192 cases in 

 horses and 3,390 in cattle. It is interesting to note that the 

 Algerian race of sheep are immune. A satisfactorj' explana- 

 tion for this striking exception has not been recorded. It has 

 been stated that a single bacterium introduced into the subcu- 

 taneous connective tissue of a guinea pig or mouse is sufficient 

 to kill it. Cats, tame and wild rabbits and hares are the next 

 most susceptible species. It is stated that dogs, pigs and foxes 

 are very slightly susceptible. Rats, fowls and pigeons are 

 reported to be immune. Fish and amphibia are rarely 

 attacked. 



§ 121. Channels of infection. Three common modes 

 of infection are recognized for anthrax, namely : through the 

 digestive tract, by the skin and by the lungs. In cattle the 

 infection seems to be largely through the alimentary canal ; 

 in horses and sheep by the skin or digestive tract ; in men 

 through wounds of the skin and the respiratory tract. 

 Although these are the usual methods there are many excep- 

 tions with each species. 



I. Infection tliroug/i the alimentary canal. This is the 

 more common mode of infection in cattle. The resulting 

 disease has been designated by various names, among which 

 are "intestinal anthrax," "fodder anthrax," "spontaneous 



