54 DISEASES OF THE LUNGS 



as irritants to the mucous membrane and thus favor the 

 development of infection which leads to bronchopneumonia. 



(c) Cold, damp, changeable weather is a very important 

 predisposing factor inasmuch as chilling the surface of the 

 animal's body modifies the circulation and the secretions of 

 the mucous membrane, reducing its resistance, as well as the 

 general resistance of the body. This favors the growth of 

 infection which may be already present. The effect of cold, 

 damp weather is well shown by the greater incidence of the 

 disease in the winter and spring months. Young puppies, 

 especially, are quite frequently affected with bronchopneu- 

 monia when kept in cold, damp and poorly ventilated kennels. 



(d) Bronchopneumonia is frequently secondary to specific 

 infections (distemper, etc.) which reduces the general as well 

 as the local resistance. 



(e) Inflammation of other parts of the respiratory system 

 may produce bronchopneumonia by an extension of the 

 inflammation. This is especially true of acute bronchitis 

 which by extension at first produces a capillary bronchitis 

 and later a bronchopneumonia. 



(/) During the course of some diseases (nephritis, endo- 

 carditis, diabetes, valvular insufficiencies, sarcomas and 

 carcinomas), the heart action is disturbed, the vasomotor 

 nerve is enfeebled, both of which reduce the resistance to 

 infection. Young puppies infested with parasites, which 

 interfere with the general nutrition, frequently develop 

 bronchopneumonia from the reduced resistance to infection. 



(g) Infectious material from the mouth and the nasal 

 passages which reach the bronchial tubes and alveoli will 

 produce a bronchopneumonia. 



Possibly in no other disease do lessened powers of resist- 

 ance of the animal, from whatever cause, play such an impor- 

 tant part in determining the inception. 



Pathology.— The process in bronchopneumonia is associated 

 with bronchitis, and indeed almost always starts with an 

 inflammation of the smaller bronchioles, which then spreads 

 to the adjacent alveoli. The exudate is at first serous and 

 contains a few erythrocytes, but more numerous white cells. 

 There is also a large number of mononuclear cells with clear 



