F. S. BILLINGS 
243 
and why by milk-cows other delicate parts of the cutis were not 
complicated as well as the udder. I have previously mentioned 
that in those seldom cases where non-milking calves, or young 
animals and bulls were complicated by the disease, that in almost 
all cases it was possible to prove that the animals in question had 
been a short time previously infected by diseased milk-cows. 
As we have already concluded that an infectious disease like this, 
which appears so seldom, and then only sporadic in single cases, 
or as an enzootic as limited to stables or droves, must necessarily 
descend from other forms of variola ; as we have excluded all 
other genetic points except variola humana vera, or humanised 
vaccine, from our consideration and have shown that although 
variola vaccina may indeed exceptionally descend from variola 
humana vera, there now remains only humanised vaccine from 
which to derive the origin of the original or genuine bovine 
variola. Having narrowed our conclusion down to this one point, 
it is not difficult to comprehend why variola vaccina does not as¬ 
sume an epizootic character; why its processes are limited almost 
exclusively to the mammae of the cow; why it appears mostly dur¬ 
ing lactation and in Spring and early Summer; and why the 
eruption appears in such an irregular manner; why the so-called 
original bovine variola appears mostly during Spring and early 
Summer—at the legal time of vaccination; why it appears only 
upon the udder of milk cows, and then only during the lactation 
period ; and why the development of the variola from self-infec¬ 
tion is generally irregular, all find a simple explanation in that 
the vaccine contagium of the human protective variola is acci¬ 
dentally conveyed to the udder of the cow by manipulation of 
milking by the hands of milkers which have previously been in 
relation with the inocul ted pustule of children. 
Therefore genuine bovine variola — v. vaccina — generates, or 
oices its origin , at present in those countries where vaccination and 
re-vaccination of man is practised , to the human proctive inocula¬ 
tion of variola. 
The following may serve to substantiate the above : 
1. Osiander describes a case of accidental infection of a cow by 
a boy who had been vaccinated but a short time previously. 
