604 INFECTIOUS DISEASES 



them with the virulent saliva, or an emulsion of the cornu 

 ammoni's, medulla oblongata, and some other portions of 

 central nerve tissue. The most satisfactory results are 

 obtained by injecting some of the virus under the dura 

 mater of the brain or cord. The same inoculation may be 

 made into the anterior chamber of the eye, or into the 

 muscles, but the results are not so certain. Injection of 

 the virus into or around the peripheral nerves has produced 

 the disease quite constantly. Scarification of the skin and 

 rubbing the virus on the area has produced positive results 

 only in about 40 per cent, of the cases. Other methods of 

 inoculation have been less successful. Birds may be infected 

 by inoculation. 



Natural Infection.— Eabies is produced in practically all 

 cases by the victim being bitten by a rabid, animal, intro- 

 ducing the virulent saliva into the wound, to come in con- 

 tact with the nerves, muscles, or subcutaneous tissues. 

 Rarely are cases produced by the infectious agent being 

 licked from wounds, or from contact with lesions on the skin . 



Pathogenesis.— When the virus is introduced into some 

 part of the body through a bite by another animal, or by 

 inoculation artificially, it is supposed that it follows the 

 course of peripheral nerve fibers along which it is carried 

 to the central nervous system. The explanation of the 

 development of the two types of the disease is explained 

 by the path of travel to the central system, whether it 

 reaches the brain, medulla oblongata, or the spinal cord. 

 After the virus reaches the central nervous system to pro- 

 duce irritation on certain groups of cells, it is then centrifu- 

 gally distributed to different parts of the body. It reaches 

 the salivary glands, which favors the development of the 

 virus, increasing the secretion of the glands, and then is 

 further disseminated through the saliva. The period of 

 incubation of rabies is quite variable. The virus after 

 being introduced into a wound may remain in a dormant 

 state for some time before reaching the central nervous 

 system. The variation in susceptibility of animals in the 

 virulency of the infection, and the method of the dissemina- 

 tion of the virus in the body naturally make the period of 



