THE LUNG PLAGUE. 23 



A dairyman, especially in a large town, may have bad pleuro-pneumo- 

 nia among- liis cattle, which had subsided, and his stock, composed of 

 animals that had withstood the disease, might be regarded as healthy. 

 But some still discharge a degree of poison and infect the atmospliere, 

 and a newly bought animal dates the period of the incubation of the 

 malady from the moment it entered the stable. 



The incubation of the disease may be said to vary from eight or nine 

 days to three or four months. In the inoculated malady the exudation 

 commences sometimes as early as the fifth day, more commonly about 

 the ninth or twelfth, and it may be as late as thirty and forty days. In 

 the disease communicated by cohabitation a cough, to which very special 

 attention was drawn by the experiments of the French commission on 

 contagion, supervenes about the ninth day and later. It is usually 

 noticed by cow-feeders, who buy cows which have just calved, that they 

 drop with the disease about the time they should manifest oestrum, that 

 is to say, six weeks after their admission. 



There are false and true periods of incubation of the lung plague, 

 and this has been overlooked too much in descriptions of the disease. 

 The actual incubation is from the period of contamination, by contact or 

 inoculation, to the moment that a special morbid change commences. 

 Our means of observation have not been exact enough, and it is very 

 desirable thatthermometric observations should be made on experimental 

 animals, and these, with the ordinary phenomena derived by auscultation , 

 &c., will assure us of the actual length of the stage of the lung disease 

 which is unattended by any appreciable sign. We shall then know the 

 true period of incubation. The false periods of incubation are those 

 derived by persons from observing an animal to sicken, say four months 

 after purchase, and drawing- the conclusion that that represents the in- 

 cubation stage. As a rule in such a case two or three latent instances 

 of the disease have preceded the obvious one. Then, again, the period of 

 incubation is not usually stated correctly by farmers, as they overlook 

 the first signs of the disease, which occur several days before cessation 

 of appetite, secretion of milk, &c. 



Invasion of the huig plague is characterized by local phenomena which 

 most fre(iuently sliow themselves by the cough already referred to. 

 With one of Casella's self-registering thermometers it will be found that 

 in an infected herd some animal or animals in apparent health, which no 

 one suspects to be diseased, will manifest a temperature of 104° or 105° 

 Fahrenheit. I have never seen a case in which, when the teinijerature 

 was thus elevated, I could not detecit friction sounds, loud respiratory 

 murmurs, especially at the lower part of the trachea- and involving one 

 lung". It is not a little remarkable to notice the want of faith of some 

 persons who watch the separation of such cattle, with great doubt as to 

 the correctness of the observation. In rinderpest the elevation of tem- 

 perature occurs before all other signs, and to a less marked extent this 

 is the same with splenic fever; but in iileuro-pneumonia there is reason 



