Microbic Diseases Individually Considered. 305 



course of an autopsy. Inter-placeiitary transmission 

 has not been established ; cases of such transmission 

 which have been brought forward have not been 

 verified. 



The period of incubation is very variable ; the dis- 

 ease most frequently appears in the course of the 

 first two months after the bite, but it may appear 

 after a few days as well as after several mouths. 

 These diiFcrences depend upon the more or less easy 

 propagation of the virus. Absorption takes place 

 chiefly by the nerves ; in fact, inoculation in a nerve 

 trunk induces rabies more rapidly than its insertion 

 in the connective tissue at a corresponding point, al- 

 though less quickly than when introduced into the 

 cranial cavity. The virus, therefore, seems to vege- 

 tate in the nerve and progress toward the cerebro- 

 spinal center, thence radiating along the nerves. 



After inoculation in the sciatic the primary rabic 

 symptoms indicate changes in the lumbar cord, the 

 cervical cord and the medula being only attacked at 

 a later stage. In one case in the guinea pig the dis- 

 ease was limited to paraplegic symptoms alone ; by 

 interrupting the continuity of the spinal cord at the 

 level of the dorso-lumbar region the dorso-cervical 

 cord was protected from the action of the virus. 

 Some cases in man which have been carefully ob- 

 served support to some extent this view as to the 

 propagation of the virus of rabies: after a bite on the 

 right arm the nerves of this arm, inoculated along 

 with those of the left arm, alone showed themselves 

 virulent. Incubation should therefore be shorter in 

 proportion as the length of nerve to be traversed be- 

 26 



