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Mr. G. F. Dowdeswell. 



V. On the Occurrence of Infectivity in the Tissues after Inoculation. 



The period at which the tissues of an animal inoculated may 

 become virulent, or the bite of a dog be infective, is of importance, 

 and as yet there are no observations on record to enable us to form an 

 opinion on this point. 



I had found in numerous experiments that if a rabbit was killed 

 upon the termination of the incubation period, on the appearance of 

 the first appreciable symptoms, its medulla was as actively infective 

 as that of an animal which had died after the disease had run its full 

 course. 



To determine at what period this infectivity is developed I inocu- 

 lated five rabbits, A, B, C, D, aud E, intracranially in the usual 

 manner from a medulla of six to seven days' incubation period. 



Of these A was killed towards the termination of the 2nd day, 

 about 44 hours after inoculation, and from its cord two others, A 

 2 and 3, were also inoculated intracranially. Another animal, B, was 

 killed at the expiration of the 4th day, and B 2 and 3 were similarly 

 inoculated. A third, C, first showed symptoms of infection towards 

 the close of the 7th day, about 164 hours after inoculation ; it was 

 thereupon killed, and C 2 and 3 were inoculated intracranially. D 

 and E, which developed symptoms during the same day as C, were 

 allowed to die in the regular course of the disease ; the one was found 

 dead on the 10th, the other died during the 11th day, with typical 

 symptoms and appearances. From the medulla of this latter two other 

 animals, E 2 and 3, were inoculated. 



Of these rabbits, A 2 and 3 as well as B 2 and 3 were altogether 

 unaffected, with the exception of a slight and transient rise of tempe- 

 rature on the 5th day in A 2, which was probably accidental. 



C 2 and 3 developed symptoms by the 7th day, which took their 

 usual course. No. 2 was found dead on the morning of the 12th day, 

 No. 3 dying during the same day. 



D 2 and 3 showed an incubation period of six to seven days, and 

 died shortly afterwards. 



From this it appears that the spinal cord of an infected animal is 

 not itself in anywise virulent till towards the close of the incubation 

 period, concurrently with the appearance of the first symptoms of 

 constitutional disturbance. I think we may conclude from this that 

 the virus is latent at the site of inoculation till this period, when, 

 somewhat suddenly, it bursts forth and pervades the tissues. In the 

 case of bites from rabid animals this seems to suggest the possible 

 utility of excising or deeply cauterising the wound, even at a subse- 

 quent period, and throws great doubt upon the authenticity of those 

 cases where hydrophobia has been said to have been occasioned by 

 the bite of an animal, which itself remained unaffected for a consider- 



