INOCULATION FOR PLEURO-PNEUMONIA IN CATTLE. 161 
pox, rabies, and many others, all of which produce their like, 
and are figured forth in some especial organ of the body. 
The inoculations of pleuro-pneumonia are made then, as 
we have seen, in the belief that this disease is highly conta- 
gious, and spreads itself from that cause, as well as the other 
special causes of an epizootic; and that the operation en- 
genders a peculiar state of the system, which, without 
imparting the disease itself to the animal, gives immunity 
against all the causes which produce it. With regard to 
attempts being made to control epizootic diseases of various 
kinds, I may here remark that Dr. Layard, a celebrated phy- 
sician, wrote an essay in 1757, strongly recommending the 
inoculation of cattle to prevent their falling a sacrifice to a 
destructive malady which at that time prevailed in this 
country. It does not, however, appear that beyond a few 
experiments the practice was adopted, although these ino- 
culated animals were said to have been placed amidst the 
infection without sustaining injury. 
I have before alluded to the interest shown by the Belgian 
Government in this matter, and I have now to observe that 
in the early part of this year two diseased cows were sent by 
order of the Minister of the Interior to Hasselt, to be placed 
with six inoculated animals, the property of M. Willems, sen. 
Eight days afterwards these two cows died, but the six inocu- 
lated animals had remained well down to the time of my visit. 
Two other cows were inoculated, and subsequently sent to the 
farm of M. De Moulin, near Hasselt, and placed with thir- 
teen of his cows then ill. These two animals continued 
unaffected, while, of the thirteen, nine died, and four were 
restored by medical treatment. I went over to this farm and 
saw the cows belonging to the Government, and I ascer- 
tained that M. De Moulin had seventeen cows origin ally, four 
of which, although not then inoculated, escaped the malady . 
It is true, these four animals were subsequently inoculated, 
and when I was there no disease had existed for three weeks ; 
but still their escape, at the time the thirteen cows were ill, 
militates against inoculation being the sole protection of the 
Government cows. On inspecting the cattle of the different 
distillers, I found several who had objected to have the ope- 
ration performed, and their animals had during the summer been 
as free from disease as the others . 
All parties agree that they have most disease in the winter, 
when the town is fullest of cattle, and when the secondary 
causes I have named are in active and vigorous operation. It is 
also admitted that in some summers since 1836, they have 
had as little disease as during the past. Similar things have oc- 
curred in the experience of most persons, and are not without 
xxvi. 22 
