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from human small-pox, it does not appear necessary to resort to
the cow as an intermediary. One of the earliest experimenters
who succeeded in variolating the cow, Dr. Thiele, of Kasan,
described a method of storage and dilution of small-pox virus
whereby he was enabled to cultivate lymph giving results indistinguishable
from vaccine. Dr. Walker, who carried on a large
vaccination practice in London, in the beginning of the century,
appears to have entertained similar views, and practised the
dilution with water of the small-pox virus.—(Memoirs of Lettsom,
Vol. iii., p. 351.)
Adams, in 1805, had already succeeded in obtaining perfect
vaccine results, without rash, with small-pox lymph taken from
a mild variety of that disease. Guillou, in 1826, again records
the fact that all the local appearances of vaccination could be
obtained with lymph of undoubted variolous origin. Indeed,
results approximating to these appear to have been arrived at by
some inoculators in the previous century, who claimed to give
small-pox without Fever or eruption, and with no other symptoms
than those occurring on the inoculated arm; it was, however,
pointed out that such modified variolation did not give the same
immunity as that which usually occasioned an eruption.
While it is probable, then, that the insertion of small-pox
matter into the skin of a calf can produce vesicles similar in some
cases to those obtained by the inoculation of cow-pox matter, we
are not aware of any evidence to show that the inoculation of the
Pox of the cow on the human skin has ever produced small-pox.
In this sense then cow-pox and small-pox are not convertible,
and we think it is incorrect to speak of cow-pox as the small-pox
of the cow.
It is impossible now to distinguish the various stocks of
vaccine in use, it is, however, clear that much of that now
current in this country and abroad is not derived from cow-pox
at all, and probably still less is derived from that special variety
of cow-pox which Jenner regarded as the true or protective