DISEASES OP THE BLOOD. 131 



Pleueo-pneumonia zymotica, vgI Contagiosa, vel Exu- 

 dativa — " Lung disease.'' Pleuro-j Perijpneumonia is a 

 specific disease affecting only horned cattle (some say 

 also the deer), spreading with rapidity in consequence of 

 its highly infectious characters, and causing remarkable 

 changes of the lungs and pleura. At first introduced into 

 this country by importation of diseased animals, it has 

 now become domiciled here, and destroys large numbers of 

 British cattle. Sometimes a case of apparently sporadic 

 pleuro-pneumonia occurs in a neighbourhood, and results 

 in an enzootic outbreak. The animal first affected has, 

 perhaps, recently arrived in this part of the country, her 

 history being unknown ; or, having been purchased from 

 a known farm, this on inquiry may turn out to have been 

 invaded by the disease. Unfortunately, the period of incu- 

 bation of pleuro-pneumonia is long, ranging even from two 

 weeks to two months, or even more than six months (Walley). 

 While this lasts, changes are going on in the lungs, and 

 certainly during the later periods of incubation the dis- 

 ease is communicable from one animal to another. The 

 general means of communication is by infection {i.e. through 

 the air). Many animals in a herd manifest immunity, but 

 beasts of all ages and sexes are liable to take the disor- 

 der. They may be rendered more susceptible by exposure 

 to severe weather, bad feeding, an insanitary condition 

 of cowsheds, &c., and by some authorities it has been 

 supposed that such conditions may result in spontaneous 

 origin of the disorder ; this, however, can hardly be, for 

 countries where sanitary measures for domesticated 

 animals were scarcely thought of and never carried out, 

 remained free from lung complaint. The contagium pro- 

 bably enters the system through the respiratory organs, 

 for, as we shall see, it has been determined that the 

 bronchial mucous membrane is the seat of primary lesion. 

 The blood is not seriously contaminated, for it has been 

 found that transfusion will not communicate the disease 

 (this, however, requires to be verified), and animals fed 

 on portions of diseased lungs did not take the disease, 

 showing that it is not readily communicable through the 



