322 CLINICAL BACTERIOLOGY. 



transmission of rabies has been established experimentally 

 in a small number of instances. 



Infection takes place by way of the nervous system. If 

 the spinal cord of a dog is divided transversely, and the virus 

 of rabies is injected into a nerve of the hind-paw, only the 

 cord below the point of division proves virulent after the 

 death of the animal. The reverse conditions prevail after 

 inoculation of a fore-paw. Having reached the central ner- 

 vous system from the periphery (site of inoculation or of 

 bite) through the intermediation of the nerves, the virus de- 

 scends into the peripheral nerves of the opposite side. For 

 this reason, if the disease has developed slowly, the nerves 

 of the uninjured side are also found poisonous in experi- 

 ments on animals. 



The as yet unknown excitant of rabies appears to exert 

 its influence through its metabolic products. At least, 

 according to Italian observers, the filtrate through porce- 

 lain of an emulsion of the spinal cord from animals suffer- 

 ing from rabies induces paralytic manifestations in dogs. 

 Rabies may, therefore, as suggested by Romberg, be desig- 

 nated a toxoneurosis. 



The dissemination of the virus of rabies in the course of 

 the nerve -paths explains why in human pathology the prog- 

 nosis of the disease varies so widely in accordance with the 

 number, the seat, and the depth of the bite -wounds. Every- 

 thing depends upon whether the virus gains entrance into 

 a nerve or not. Deep wounds are, therefore, much more 

 dangerous than superficial ones ; injuries in regions with an 

 abundant nerve-supply (as, for instance, the finger-pulp) 

 more so than in other parts of the body. The greatest dan- 

 ger is involved in wounds of the head and the face. From 

 these the virus of rabies quickly reaches the medulla 

 oblongata, the main seat of the disease. The morbidity 

 and the mortality of rabies (the developed disease is in- 

 curable) are, according to the most reliable statistics, about 

 1 6 per cent, of those bitten. 



Incubation. The duration of the period of incubation 

 depends upon the same factors that have been mentioned 

 as significant in prognosis. The period is the shorter the 

 nearer to the head the portal of infection is situated. The 

 usual duration of the incubation-period is from twenty to 

 sixty days. The trustworthy minimum observed has been 

 fourteen days ; the maximum, eighteen months. 



