THE VIRUS OF HYDROPHOBIA 615 



diseases, we -would strongly suspect that' it is actually present 

 in a living condition in the central nervous system, the saliva, 

 etc., which yield what we have called the hydrophobic virus, 

 for, by no mere toxin could the disease be transmitted through 

 a series of animals, as we shall presently see can be done. A 

 toxin may, however, be concerned in the production of the 

 pathogenic effects. Remlinger found that death with paralytic 

 symptoms followed the injection of filtered virus, but that the 

 nervous system of the dead animals sometimes did not reproduce 

 rabies. He explains this occurrence by supposing that under 

 such circumstances the filtrate contained a toxin but not the 

 actual infective agent. The resistance of the virus to external 

 agents varies. Thus a nervous system containing it is virulent 

 till destroyed by putrefaction ; it can resist the prolonged 

 application of a temperature of from — 10° to - 20° C, but, 

 on the other hand, it is rendered non-virulent by one hour's 

 exposure at 50° C. Again, its potency probably varies in nature 

 according to the source. Thus, while the death-rate among 

 persons bitten by mad dogs is about 16 per cent., the corre- 

 sponding death-rate after the bites of wolves is 80 per cent. 

 Here, however, it must be kept in view that, as the wolf is 

 naturally the more savage animal, the number and extent of the 

 bites,- i.e., the number of channels of entrance of the virus into 

 the body and the total dose, are greater than in the case of 

 persons bitten by dogs. As we shall see, alterations in the 

 potency of the virus can certainly be effected by artificial 

 means, such as drying, heating, and applying chemical agents. 

 Various attempts have been made to make cultures from 

 the hydrophobic virus, but convincing results have not been 

 obtained. 



In 1903, Negri described certain bodies as occurring in the 

 nervous system in animals dying of rabies to which much 

 attention has since been devoted, and regarding the significance 

 of which opinion is still divided. As Negri's observations have 

 been generally confirmed, and as it is probable that the 

 occurrence of the bodies is specific to the disease, and that their 

 recognition is of value for diagnosis, we shall describe the 

 methods of their demonstration. 



The method of Williams and Lowden is to take a piece of the brain 

 tissue, to squeeze it between a slide and cover-class, and, sliding off the j 

 latter, to make a smear which is then fixed in methyl-alcohol for five' 

 minutes and stained by Giemsa's stain (p. 113) for half an hour to three 

 hours ; the preparation 16 then washed in tap water lor 2-3 minutes and 

 dried. For rapid work, after fixation, equal parts of distilled water and 

 stain are used instead of the more dilute mixture. 



