66 Manual of Veterinary Microbiology. 



Rabies, a spontaneous* disease of the dog, is inoc- 

 ulable to all species of martimals and to birds, intra- 

 cranial inoculation being always successful, whilst 

 hypodermic inoculation gives only variable results. 



Bacteridian charbon develops naturally in cattle, 

 sheep, and horses, experimentally in all the domesti- 

 cated mammals. 



Influence of the individual. — All the individuals of 

 any species susceptible of contracting a microbic 

 disease do not take that disease when they are ex- 

 posed to the contagion ; some of them are less sus- 

 ceptible than others and a few may even be absolutely 

 refractory. 



Influence of age. — Strangles, and distemper of dogs 

 are diseases of youth; symptomatic charbon only ap- 

 pears in cattle of from six months to four years and 

 is with difficulty inoculated to the young calf ; guinea 

 pigs are the more susceptible to charbon the younger 

 they are. Pigs of less than four months are much 

 less susceptible to rouget than adults ; hence, only 

 very young pigs should be vaccinated against this 

 disease. 



4. Influence of heredity. — Certain predispositions are 

 inherited; for example, that of children born of con- 

 sumptive parents, to contract tuberculosis. 



5. Influence of depressive causes. — All conditions 

 which have a debilitating effect on the organism fa- 

 cilitate microbic invasion. Pasteur has shown that 

 lowering the temperature of fowls inoculated with 

 charbon is followed bv the evolution of the disease in 

 these animals in spite of their natural immunity. 



* [Acquired by transmission from its own kind. — D.] 



