REPORT OF THE ROYAL VACCINATION COMMISSION. 683 



As has been urged in another place, there are no adequate reasons 

 leading us to believe that in the human subject the small-pOK virus and 

 the cow-pox virus can so act on each other as to form a hybrid disease. 

 But this does not preclude the view that, accepting the conclusion that 

 the body of the cow has the power to convert small-pox into vaccine, the 

 virus may exist for a while in a phase in which, while ceasing to be 

 typical small-pox, it has not yet fully acquired the characters of vaccine, 

 and we may regard Klein's results as illustrating this. In some of the 

 experiments — for instance, those of Ceely and Voigt — the results obtained 

 with the lymph of the vesicle produced by the inoculation of small-pox 

 give rise to the suspicion that the lymph had small-pox qualities, as seen, 

 for example, in the case of Ceely's assistant, Taylor ; but the facts cannot 

 be said to be more than suspicious — they are not decisive. Moreover, 

 admitting that the vesicle itself in such cases was the result of the trans- 

 formed virus, some not transformed old virus might stiU remain dormant 

 in the wound, and might be present in the lymph of the vesicle, mixed 

 with the transformed and generating virus ; this old virus might have 

 happened to be in excess on the point of the lancet which wounded 

 Taylor. 



STTuiU-pox Vaccine— Cow-pox Vaccine — Hmse-pox Vaccine — Cattle- 

 plague Vaccine — Sheep^ox Vaccine. 



Taking all the various facts into consideration, we seem led to the 

 provisional conclusion that under certain conditions the tissues of the 

 cow are able to transform smaU-pox into vaccine, that these conditions 

 may be such as to lead to the transformation being sudden and complete, 

 that under certain other conditions the transformation may be gradual 

 and incomplete, and that under certain other conditions (and these seem 

 most commonly to obtain) the transformation into vaccine does not take 

 place at all. But what the above conditions are has not as yet been 

 clearly made out. It has been suggested that one condition favourable 

 to the transformation is extreme youth of the subject : to effect the 

 change the animal used should he a calf of not more than three or four 

 months old ; but this is not definitely proved. 



Until these favourable conditions have been clearly recognised, so that, 

 the conditions being fulfilled, the transformation will always be secured, 

 the conclusion cannot be regarded as indisputable. Moreover, it must 

 be borne in mind that effects more or less closely resembling a vaccine 

 vesicle have been at various times obtained by various observers through 

 inoculating man or the cow or another animal with material other 

 tl^an that obtained from the pustules of the small-pox of man. Much 

 discussion has taken place concerning the "grease" of the horse which 

 Jenner believed to be the origin of the cow-pox of the cow. Without 

 entering into any discussion of the matter, it may be said that investiga- 

 tion has shown that horses do suffer from a malady which, transferred to 

 the cow, gives rise to a vaccine identical apparently with that produced 

 by the inoculation of the natural cow-pox. Hence this malady is spoken 

 of as the "horse-pox," and some cases at least of so-called "grease" 

 appear to be cases of this horse-pox. But it is at least not proved that 



