Microbic Diseases Individually Considered. 307 



transmitted by intra- venous inoculation, demonstrate 

 the possibility ot* the absorption of the virus and its 

 transmission by the circulatory fluids. 



Attenuation and Vaccination. — The virus of rabies is 

 not absolutely fixed; its passage through the organ- 

 ism of the rabbit exalts its virulence, as we have seen 

 above, whilst its inoculation to the ape enfeebles it. It 

 becomes acclimated in the ape after three generations 

 and then requires an incubation of twenty-three 

 days, the incubation for natural rabies being only 

 eleven days. The fixed virus of the ape only rarely 

 communicates the disease to the dog by intra-cranial 

 inoculation, and intra-venous inoculation is always 

 inoffensive ; this virus can be ifsed to vaccinate the 

 dog. 



Babes has shown that the virus of rabies introduced 

 into the lymph sac of the frog becomes progressively 

 attenuated until, after a certain time, it is capable of 

 acting as a vaccine for the dog. The lymph of the 

 frog removed from the body and mixed with an 

 emulsion of a virulent cord also attenuates the ac- 

 tivity of the latter. 



Attenuation by desiccation. — A virulent rabic cord 

 progressively loses its activity by desiccation in the 

 air. This attenuation manifests itself by retarding 

 the appearance of the disease, — .increasing the dura- 

 tion of incubation ; thus, after two days' desiccation 

 the fixed virus of the rabbit has not changed, and 

 produces the disease in rabbits after seven days; after 

 three to five days the incubation lasts for eight days; 

 after six days it is extended to fourteen days ; after a 

 desiccation of more than seven days the disease is no 

 more communicated to the rabbit. ^-a-===-._ 



ff OF THR ^ 



I "UNIVERSITY 



