68 



Mr. G. F. Dowdeswell. 



and only very exceptionally by any reaction of the animal inoculated, 

 is shown by the circumstance that, however many animals, of the 

 same species, are inoculated from the same source, this period gene- 

 rally shows no variation at all in them, though the duration of the 

 disease, and consequent occurrence of death, is evidently dependent 

 mainly upon the age, condition, and vigour of the subject. 



VII. Preservation of the Virus and Methods of Modification. 



On the occurrence of septic decomposition in the medulla the virus 

 is destroyed, but M. Pasteur has stated that by removing portions of 

 virulent medulla with precautions against contamination, and sus- 

 pending them in an atmosphere of pure carbonic acid, their infectivity 

 is retained unimpaired for some weeks. 



I have not, however, found this to be the case ; I have in several 

 experiments carefully removed a portion of the cord of a rabid 

 rabbit, passing it and the ligature to which it was attached through 

 the flame of a spirit-lamp and suspended it in a vessel, previouly 

 disinfected, plugged with sterilised cotton-wool, and kept saturated by 

 a constant current of C0 3 , filtered through cotton- wool. 



In every case I found that within a few days the virus was mate- 

 rially modified, and soon completely destroyed, the rapidity of the 

 change probably depending upon the temperature. In summer on 

 the third day this diminution in virulence is apparent in the results of 

 inoculating rabbits with it. Septic microbes, however, do not develop 

 in the medullas, as long as kept in this manner. 



I consequently find this method unsuitable for preservation of the 

 virus for even the shortest period. 



The basis of M. Pasteur's present methods of protective inoculation 

 consists in the asserted progressive modification and ultimate extinc- 

 tion of the virus which is produced by suspending a portion of infective 

 medulla in a current of dry air. The methods adopted are to take 

 out a portion of the spinal cord of a rabid rabbit soon after death, 

 then passing it lightly through the flame of a spirit-lamp,* in order to 

 destroy any septic germs which may have fallen upon its surface, to 

 suspend it by a ligature similarly flamed, in a previously sterilised 

 bottle, with tubulature at top and bottom, plugged with cotton-wool, 

 and containing a quantity of caustic potash. 



Thus prepared the cords are gradually dried ; the potash, absorbing- 

 all moisture, prevents any development of septic organisms quite 

 effectually. A portion of a cord dried for the length of time required 

 for inoculation is then triturated with bouillon, strained as before 

 described, and injected subcutaneously. 



* The sterilisation however is superfluous, inasmuch as saprophytes do not 

 develop in dry air. 



