704 INFECTION AND IMMUNITY. 



neither gross nor microscopic changes which are 

 characteristic. 



on A great deal of experimental work which can not 

 \erves. be given in detail shows conclusively that the virus 

 is conveyed to the central nervous system by means 

 of the peripheral nerves. The conditions then are 

 similar to those in tetanus with this exception : In 

 hydrophobia the living virus reaches the central 

 nervous system, whereas in tetanus the bacilli re- 

 main at the site of the wound. This condition ex- 

 plains the shorter incubation period in hydropho- 

 bia, as in tetanus, when the infection atrium is 

 near the central nervous system (e. g., face). When 

 the infection is introduced into any particular 

 part of the body surface, the virus is first demon- 

 strable in the corresponding segment of the cen- 

 tral nervous system. Although transmission by 

 the nerves is the rule, infection may be accom- 

 plished in rabbits by intravascular injection. On 

 the whole, however, infection is closely associated 

 with the wounding of nerves. It has indeed 

 been shown that if wounding of nerves is entirely 

 avoided, as in intraperitoneal injections into rab- 

 bits (Marx) the full virulent nervous tissue may 

 be used for immunization. A single injection of a 

 large quantity brought about immunity in twelve 

 days. 



The muzzling of dogs is a general prophylactic 

 measure, which should be enforced in communities 

 in which hydrophobia is known to occur. No mat- 

 ter how thoroughly the cauterization and antisep- 

 tic treatment of wounds is carried out it can in no 

 case be depended on to destroy the virus. Even 

 within five minutes the virus may be carried to a 

 point which is beyond the reach of the cautery. In 



