450 INOCULATION FOR PLEURO-PNEUMONIA IN CATTLE. 
It will be sufficient for the present to make but one or two 
comments on these conclusions : and firstly, on (£ the suppo 
sition” contained in the 11th section, to the effect that 
animals dying of Pleuro-pneumonia, subsequent to inocula- 
tion, have at the time of the operation the disease incubated 
in their systems. This is a point of some importance in the 
present inquiry, and particularly with regard to protection ; 
for while it admits that Pleuro-pneumonia is a disease which 
has, like many others, its incubative stage, still it fixes no 
limit to such stage. We might consequently infer that, in 
the opinion of the Committee, an attack of the malady, subse- 
quent to inoculation, howsoever remote it may be, would not 
depend on an exposure to the ordinary causes producing it, 
but on its being incubated at that time. Indirectly, the 
committee here assert that inoculation is protective to the 
animal during the remaining period of its life. That such is 
not their opinion is seen, however, by the 13th conclusion. 
It is unnecessary here to discuss the question of the differ- 
ences in the period of incubation of different diseases. For 
the most part they are well understood, and with very few 
exceptions clearly ascertained ; rarely does the time exceed 
two or three weeks. It is evident, therefore, that the Com- 
mittee merely desire to give it as their opinion, that Pleuro- 
pneumonia, if happening within a very short time of inocula- 
tion, was lying dormant in the system of the animal when the 
operation was performed. In this view of the subject we can 
coincide ; but this leaves such cases as are named in our first 
report,* of animals attacked two months , and three months and 
a half \ after inoculation, to be accounted for only on the 
principle that they were unprotected by inoculation, and there- 
fore it is an argument against the practice. This question 
will receive further elucidation from the facts which will be 
given in the after part of the present report, and we will 
only add that no person acquainted with Pleuro-pneumonia 
would be found bold enough to affirm that the disease is 
incubated, or, in other words, is slowly advancing to maturity, 
during so long a time as two or three months, and this without 
the animal exhibiting any indications of its existence. 
The only other point in the report of the Dutch Commis- 
sioners necessary to allude to here is found in the concluding 
sentence, where the Committee observe that they do not 
“ hesitate to recommend inoculation under prudent treatment 
in every case where pulmonary disease has broken out in a 
herd of cattle or in the neighbourhood.” Would that our 
own experience enabled us to say the same : for the present, 
* See Journal, vol. xiii, p. 382. 
