PLEUROPNEUMONIA. 
823 
In nearly every instance it was ascertained that the disease 
had originated among newly-introduced stock, and afterwards 
extended to the other cattle on the farm. Precisely the same 
evidence has been obtained in respect to the majority of out- 
breaks; but it must be admitted that many outbreaks cannot 
be traced to the introduction of strange cattle — on the con- 
trary, the disease has often originated in animals which have 
been on the premises for many months. 
The report of the French Scientific Commission, pub- 
lished in 1854, contains a record of a most complete series of 
experiments, w T hich were carried out in order to decide the 
the disputed point. Animals were obtained from a district 
in which pleuropneumonia had never been known to occur; 
they were placed with three diseased cattle in a shed and 
carefully isolated. The result of the experiment may be thus 
stated. In six days after the diseased animals were intro- 
duced, several of the cows were observed to have a peculiar 
cough, although the lungs were not found to be diseased, nor 
was the appetite affected. Soon the characteristic symptoms 
of pleuropneumonia followed, and several of the animals suc- 
cumbed. The inference which the investigators drew from 
these experiments was that healthy cattle are likely to become 
affected with pleuropneumonia as the result of associating 
with cattle suffering from the disease. Of 100 which were 
submitted to the test, 20 proved to be unsusceptible ; 80 
presented symptoms, more or less marked, of being under 
the influence of the infection; and 50 of them contracted 
pleuropneumonia in a decided form. In the course of these 
experiments it was remarked that “ the transmission of 
pleuropneumonia is capable of being effected at a certain dis- 
tance, and that it was not necessary for immediate contact to 
take place before the phenomena of the disease were mani- 
fested" 
When cattle are feeding in the open fields, it is difficult to 
determine w hether contact with a diseased subject or with the 
emanations which are given off is the most deadly ; but in 
cow-sheds the observation has been repeatedly made that the 
disease does not pass in rotation from one animal to the next 
in order, but attacks them at irregular intervals. Lest this 
fact should be construed in favour of the idea of the disease 
being non-infectious, it is proper to remark that the same 
circumstance w r as noticed during the prevalence of cattle 
plague ; and it is also true in respect of foot-and-mouth dis- 
ease that animals in the cow-shed fall sick in various parts 
of the premises, instead of in the order in w^hich they stand. 
To ascertain the manner of communication of the disease, 
