460 INFECTIVE DISEASES. 



several months, and in rare cases a much longer period. The wound 

 from a bite may have healed, and may again become inflamed, 

 and symptoms follow, owing to the poison affecting the brain, spinal 

 cord, or the peripheral nerves. In the dog the disease appears in 

 two forms-^raging madness and dumb madness ; and the identity of 

 the virus in the dog and in man is shown by the fact that virus 

 from man can produce both forms of the disease in the dog. The 

 virus may be obtained by inoculation of the sahva of a rabid dog ; 

 but this method is uncertain, as other micro-organisms are present. 

 Pasteur endeavoured to obtain it in a pure state, and was able 

 to demonstrate that the spinal cord, the brain, and the nerves 

 contain the virus. It was also found that by direct inoculation of 

 the nervous system the most certain results followed. 



Bacteria in Rabies. — Cocci have been described in connection 

 with hydrophobia by Fol, Bab^s, and Dowdeswell. The cocci, it is 

 said, were observed in sections of the spinal cord of rabid dogs. The 

 descriptions given by different observers vary considerably, and there 

 is not any particular coccus constantly associated with the disease. 

 Nor have any of the bacteria been isolated from the diseased animal, 

 which were alleged to be present in stained preparations. By many, 

 hydrophobia is believed to be due to the presence of a micro- 

 organism, but at present the nature of the contagium is unknown. 



Protective Inoculation. — Pasteur found that a dog inoculated 

 under the dura-mater with virus from the spinal cord of a rabid animal 

 will develop rabies, as a rule, within eighteen days. By trephining 

 rabbits and inoculating the virus, and by, in the same way, 

 transmitting the virus from rabbit to rabbit, the incubation period 

 gradually shortens, until it is reduced to six or seven days. The virus 

 has then reached its maximum virulence in the rabbit, and is " fixed." 

 Pasteur then studied the possibility of producing immunity. The 

 medulla of a rabbit, containing the virulent virus, was suspended in 

 a glass bottle over caustic potash at a temperature of 25° 0. If a 

 number of spinal cords were thus treated, and examined from day 

 to day, it was found that they gradually lost their virulence, 

 becoming completely inert in from sixteen to twenty days. A series 

 of cords was thus obtained with diminishing virulence ; by injecting 

 subcutaneously an infusion of rabid spinal cord crushed in broth, 

 and beginning with an inert cord on the first day and using the 

 next in the series on the second day, and so on till a fresh spinal 

 cord could be injected, it was found that dogs were rendered 

 insusceptible to the strongest virus, administered by inoculation or 

 by exposing them to the bites of rabid dogs. Dogs have usually 



