Jrom an Agricultural and Veterinary Point of Vieic. 87 
other, as each was the rigorous verification, by conclusive ex- 
periment, of a preconceived idea, upon which he always worked. 
" Nothing can be done," he asserted, " without preconceived 
ideas ; only there must be the wisdom not to accept their 
deductions beyond what experiment confirms. Preconceived 
ideas, subjected to the severe control of experimentation, are 
the vivifying flame of scientific observation, while fixed ideas 
are its danger." 
The fact that certain contagious diseases, as a rule, affect 
an animal or a man only once in a lifetime, has been known 
from time immemorial ; and this fact of non-recurrence has 
been acted upon in the case of some of these disorders, in pro- 
ducing them purposely in man and beast, in a milder form 
if possible, or, at any rate, under more favourable conditions, 
than in the ordinary accidental or natural manner. Eastern 
people — the Chinese, for example — looking upon an attack 
of small-pox as inevitable, and knowing the great mortality 
or disfigurement caused by the disease when caught through 
infection, have resorted to inoculation in order to induce a 
less serious and more tractable form at a convenient time. With 
the same object, for very many years, inoculation has been 
practised for sheep-pox in some of those countries — as Germany 
and France — where it always prevails to a more or less con- 
siderable extent. In the Russian Sieppes, also, for a long time 
experiments were made to test the advantages of inoculating 
cattle for Rinderpest ; and in recent years the same measure 
has been tried for " distemper " in dogs. In some outbreaks of 
Foot-and-mouth disease, cattle-owners have often produced this 
troublesome affection in their yet healthy animals, in order to pre- 
vent it lingering among them for a long time, and so to get rid 
promptly of what threatened to be an inevitable and more harass- 
ing visitation. And protective or preventive inoculation for the 
Lung-plague of cattle, introduced by Dr. Willems, of Hasselt, 
some thirty or forty years ago, has been very much resorted to in 
countries where that insidious and deadly pest prevails. But 
in all these instances the inoculation has been effected with the 
natural, or what we might designate the " crude " virus ; and 
therefore the danger was great that the diseases might at times 
be induced in as great virulency as when they appeared in the 
ordinary way. This has been the case especially with Cattle- 
plague inoculation, which, because of the unsatisfactory results, 
has now been abandoned ; while the benefits to be derived from 
Sheep-pox inoculations are perhaps more than counterbalanced 
by the disadvantages which attend them. 
The introduction of vaccination as a protection against small- 
pox, by Dr. Jenner, has proved an immense success, but hitherto 
