598 RABIES AND THE NEGRI BODIES 



so far as known, cannot penetrate the intact skin, but rabbits may 

 be infected through the intact nasal and conjunctival mucosa. The 

 virus cannot enter through the gastro-intestinal tract, as has been 

 shown by Nocard in his feeding experiments. The percentage of 

 infections in animals bitten by dogs suffering from rabies is variously 

 estimated, and the figures given extend over a wide range, anywhere 

 from 5 to 40 per cent. There appears to be both a racial and an 

 individual variability. The virus of hydrophobia after having gained 

 access to the body of a susceptible animal travels from the portal of 

 entrance to the central nervous system, where it spreads gradually. 

 According to the investigations of Vestea and Zagari, inoculation 

 into the sciatic nerve of the rabbit is first followed by paralysis of the 

 hind leg of the same side and the paralysis progresses from behind 

 to the anterior part of the body. When the inoculation is made in 

 an anterior extremity the progress is from in front backward. The 

 virus multiplying in the central nervous system affects the vessel 

 walls and produces around them small, round-celled inflammatory 

 infiltrations. It damages the ganglion cells, causing psychical dis- 

 turbances, increase of reflex irritability, and later degenerative 

 manifestations, with paralysis, which finally affects the respiratory 

 apparatus and so leads to death. 



Period of Incubation. One of the most remarkable characteristics 

 of hydrophobia is the great variability of the period of incubation 

 after natural infection. As a rule, this period lasts a few weeks, but 

 not infrequently may be prolonged to a few months. In dogs and 

 hogs the period of incubation is frequently shortened to ten to fifteen 

 days; in horses and cattle it is frequently from one to three months. 

 According to statistics by Roell, of 144 rabid dogs, 43 per cent, 

 developed manifest symptoms of hydrophobia within thirty days 

 after being bitten, 40 per cent, between the thirtieth to the sixtieth 

 day, 14 per cent, between the sixtieth to the nintieth day, and 3 per 

 cent, between the fourth to twelfth month. Zuendel gives the following 

 figures for 579 head of cattle: 5 per cent, in less than fifteen days, 

 23 per cent, between fifteen and thirty days, 39 per cent, between 

 thirty to forty-five days, 13 per cent, between forty-five to sixty days, 

 17 per cent, between three to six months. One animal after forty-two 

 and one after ninety-five weeks. Unusually long periods of incubation 

 in horses have been reported; by Gosswinter, twenty months; by 

 Bahr, twenty-one months; by Swain, twenty-five months; in cattle 

 by Szabo, three hundred and twenty-three days; Mieckley, three 

 hundred and twenty-seven days; Leipert, nearly twenty months; Kalt, 

 twenty-three months. Ligniere reported the case of a rabid watch dog 

 on a farm biting twenty head of cattle. Four oxen out of the twenty 

 animals bitten died after incubation periods between two and six 

 months. All four succumbed to the paralytic form of the disease, as 

 also did one cow, but only after an incubation period lasting three years 

 In man the period of incubation likewise varies considerably. Paltauf , 



