732 BOARD OF AORICULTURE. 



the aiiiiual takes, but the disease is rarely spread from the discharges 

 from the wound. Blnckleg is oWtaiiicd from the pasture or. forage, the 

 germs lieiug knowu to live for a long time outside of the body. lu- 

 rtuenza and strangles occur in epidemics because the germs live outside 

 the body and under favorable climatic conditions develop generally, thus 

 causing widespread outl)reaks at tlie same time. Hog cholera and swine 

 Itlague are both infectious and contagious, the germs live outside the 

 body and no amount of separation o.f herds will ever stamp out the dis- 

 ease. It only decreases the number of cases. The germs of tetanus or 

 lockjaAA" are to be found growing in the soil, but do not cause trouble 

 unless accidentally introduced into a closed wound. Infectious diseases 

 can not be wholly controlled because the occurrence in an animal is not 

 essential to the life of the germ. Some may be prevented by vaccina- 

 tion, as blackleg, and some have been greatly reduced by learning the 

 habits of the germs outside of the body and making these places uncon- 

 genial to their growth. 



The Causes of Disease.— The causes of disease are the indirect or pre- 

 disposing causes and the direct or exciting causes. The predisposing 

 causes are many factors which tend to render the body more susceptible 

 or to favor the presence of the exciting cause. The exciting cause is the 

 specific agent or the thing that introduces the disease. To illustrate, an 

 animal having a narrow, pinched chest may be in health, but when sub- 

 jected to the same conditions as its companions it contracts disease while 

 they do not. The lessened lung capacity has rendered the animal sus- 

 ceptible. Hogs pastured on high dry gi'ound and fed on clean feeding 

 floors are comparatively free from intestinal worms; hogs pastured upon 

 low, wet ground and in the mud are frequently infested with worms. In 

 this case the low, damp pasture has been favorable to the parasite, and 

 therefore made it possible to do harm. In one case the predisposing 

 cause was in the animal; in the other, without. 



Among the causes of disease we may brieflj' consider the following: 



Age. — Young animals are more subject to attacks of contagious or 

 infectious diseases than old. White scours, suppurative joint disease and 

 infectious sore mouths are diseases of the first few days or weeks. 

 Thumps occur early. Cholera occurs with much greater virulence in 

 those under six mouths of age than in the older. Lung worms or whoop- 

 ing cough occurs between two and four months. Swine plngue attacks 

 the older hogs. Trichinae likewise more often occurs in mature animals. 

 As a rule, the yoiuig are more subject to acute diseases and the old to 

 chronic troubles. 



Sex.— The matter of sex has little bearing on the diseases of swine 

 ether than those due to farrowing. 



Breed.— The matter of breed is of less importance in the diseases of 

 swine than in other domestic animals. Some breeds are more active than 

 others, and thereby seem to have increased resistive powers to some 



