GENERAL DISCUSSION OF DISEASE 5 



The predisposing causes are such factors as tend to render 

 the body more susceptible to disease or favor the presence of the 

 exciting cause. For example, an animal that is narrow chested 

 and lacking in the development of the vital organs lodged in 

 the thoracic cavitv, when exposed to the same condition as the 

 other members of the herd, may contract disease while the 

 animals having better conformation do not (Fig. 1). Hogs 

 confined in well-drained yards and pastures that are free from 

 filth, and fed in pens and on feeding floors that arc clean, do 



Fig. 1. — (A) side and (B) posterior view of bull showing conformation favorable to the 

 development of disease. 



not become hosts for large numbers of parasites. Hogs confined 

 in filthy pens are frequently so badly infested with lice and intes- 

 tinal worms that their health and thriftiness are seriously inter- 

 fered with. In the first case mentioned the predisposition to 

 disease is in the individual, and in the second case it is in the 

 surroundings (Fig. 2). 



The exciting causes are the immediate causes of the par- 

 ticular disease. Exciting causes usually operate through the 

 environment. With the exception of the special disease-produc- 

 ing germs, the most common exciting causes are faulty food and 



