On Rabies. 



67 



rabid street dogs. In other cases the period has been from seventeen 

 to nineteen days, which appears to be about the average, and agrees 

 nearly with that given by M. Pasteur and Prof. Frisch. 



When the virus of street rabies is passed through a sufficient 

 number of rabbits the period is further reduced to six or seven days, 

 and becomes markedly constant. In a period of about six months I 

 have carried this virus, originally obtained from M. Pasteur's Labora- 

 tory, through a series of twenty rabbits, inoculating two or more of 

 each series. In the large majority of cases the first symptoms of in- 

 fection have appeared between the sixth and seventh days, exception- 

 ally not till the eighth day, in a few instances till the ninth. Latterly I 

 have observed two cases in which the latent period was only four days. 



In one case quite recently, two rabbits were inoculated intracranially 

 from one of a Pasteurian series, that had died after a very unusually 

 short incubation period, with characteristic symptoms, bat of only 

 some hours' duration, on the fourth day after inoculation. One of 

 these so inoculated died on the third day, apparently from accidental 

 causes, the other remained unaffected and healthy till the fortieth 

 day, when it was observed to be paralysed, and was found dead the 

 following morning, with post-mortem appearances that were very 

 well marked and characteristic ; the haemorrhages in the stomach, 

 though not perceptible on the serous coats, were larger on the mucous 

 surface, though few in number, than any other I have observed, 

 almost resembling, as has been described, " crushed currants." This 

 duration of the incubation period is quite exceptional. 



From the medulla of this case two other rabbits were inoculated 

 by trephining ; they both showed an incubation period of the usual 

 length — six to seven days — with well-marked symptoms, thus proving 

 that the remarkably protracted incubation period in the above case 

 was due to some accidental cause, and that the virus had undergone 

 no permanent modification. 



I have had the opportunity of inoculating intracranially from the 

 medulla of a rabid horse, in this case with an incubation period of 

 seventeen days, and from a rabid ox, as also from a case in man, in 

 all of which it was about the same, and the symptoms of infection and 

 post-mortem appearances were identically similar to those following 

 inoculation from the dog or rabbit. 



I have also inoculated rabbits from the medulla of a furiously rabid 

 cat,* which had been itself inoculated from a street dog. In this case 

 the incubation period — in the rabbits — was between seventeen and 

 eighteen days, with the regular symptoms and post-mortem appear- 

 ances. 



That in inoculating rabbits intracranially, the duration of the in- 

 cubation period is usually determined by the activity of the virus, 



* The same animal that bit the man, Joseph Smith, hereinafter mentioned. 



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