608 MANUAL OF MODERN FARRIERY 



suffer from symptoms simulating those of rabies, and 

 formerly when human beings were bitten, it was 

 impossible to determine whether the dog had been 

 suffering from rabies or not. We are indebted to 

 Pasteur for the only reliable test which can be applied, 

 and we are now in a position, when a human being 

 is bitten by a dog supposed to be, but not really, 

 rabid, to remove all cause for the anxiety which 

 would otherwise remain for months and even years. 

 " Pasteur found that a dog inoculated under the 

 dura-mater (covering of brain) 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 in- 

 cubation 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 C. If a 

 number of spinal cords were thus treated, and ex- 

 amined 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 were 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 an incubation period of 



