1902.] The Inter-relationship of Variola and Vaccinia. 133 



In each of the separate series of experiments the human small-pox 

 lymph or pulp was first inoculated directly on calves, and in every 

 instance, so far as could be observed, with altogether negative results. 

 But with monkeys success was as invariably obtained, and when, after 

 one or more passages through this animal, the contents of the local 

 inoculation vesicles were employed for insertion on the calf, an effect 

 was now produced which, after two or three removes in that animal, 

 was indistinguishable from typical vaccinia. 



Moreover, from the contents of vesicles raised in this manner on the 

 calf, a number of children have, in turn, been vaccinated, some of 

 whom were afterwards kept under observation for as long a period 

 as a couple of months. 



Every such vaccination " took " normally, and in no case was any 

 bad result subsequently observed by nryself, or reported by the 

 parents of the children ; no " generalisation " of the eruption occur- 

 ring in any instance. 



In conclusion, I desire to call attention to the somewhat remarkable 

 fact that a mild and strictly localised form of small-pox, such as is 

 induced in the monkey by the inoculation of material from cases of 

 the generalised disease in man, should, when transferred to the calf, 

 "take" readily with the production of a vesicular eruption of non- 

 infectious character in that animal, whereas it is well known that 

 successful transference of small-pox direct from man to calf can only 

 be accomplished with the utmost difficulty. 



The experimental results obtained in the course of the research, an 

 account of which has been set out in this paper, all tend, then, to 

 confirm the view that the vaccinia of Jenner's time was derived, in all 

 probability, from a comparatively mild form of human small-pox. 



In addition, I think it will be admitted that the work has afforded 

 conclusive evidence of the essential identity of the virus of small-pox 

 and cow-pox or vaccinia. 



