SUMMARY OF EVIDENCE ON PLEURO-PNEUMONIA. 289 



to the other. Where it has been asserted that the infection has 

 been carried long distances, it has not been proved that it was 

 not imported into the herd by means of a diseased animal. 



The general opinion seems to be that pleuro-pneumonia is 

 not a very infectious disease, except where animals are actually 

 housed together. 



3. About one-fourth of the witnesses give it as their opinion 

 that the disease may be contracted by a healthy animal by its 

 being put into a stall or byre, or even a held, which had pre- 

 viously been occupied by a diseased animal. Nearly an equal 

 number either doubt or deny the possibility of conveying the in- 

 fection in that way ; but it is the universal practice to act on 

 the supposition that a place may retain the infection and be 

 capable of communicating it, and therefore some kind of disin- 

 fecting process is had recourse to. These precautionary mea- 

 sures are of various kinds, and are usually so very defective that 

 it is evidently a matter of no importance whether they are 

 carried out or not. 



4. In only five instances is the opinion expressed that the 

 infection can be carried by the clothes or persons of attendants, 

 or by means of dogs, rats, or other animals passing from the 

 precincts of diseased to those of healthy animals, while the 

 great majority are strongly of opinion that the disease cannot 

 be propagated in that way. Instances are recorded in which 

 the attendants passed constantly between diseased and healthy 

 animals, feeding and milking them, without conveying the in- 

 fection. It is curious to note that some of those who deny the 

 possibility of infection being carried in the clothes of attendants, 

 yet hold the view that the stall in which a diseased animal has 

 been kept, and its fodder, litter, and dung may retain and con- 

 vey the infection. It is scarcely necessary to say that such 

 views are entirely at variance with all that is accurately known 

 regarding the propagation of infectious diseases. 



5. The length of time during which the disease may remain 

 latent or undiscovered in an animal is a matter regarding which 

 there exists very great difference of opinion, but as the opinions 

 entertained are the product of actual experience, they are 

 deserving of careful consideration. Twenty-two report that 

 they have never known the disease to be latent for more than 

 two months ; twenty-six report instances in which it has been 

 latent for about three months ; and forty-two report that either 

 in their opinion or in their experience it may be present and yet 

 not manifest itself for four months or more. The usual term of 

 latency, or what is called the incubative period, is regarded as 

 from four to six w^eeks. When the disease does not break out 

 in a herd until several months have elapsed, it has been found 

 to be due to the importation into the herd of an animal that 



VOL. XX. T 



