158 DISEASES OF SWINE AND OTHER ANIMALS. 



Only one of them liad then died. I might go on and illustrato by a good 

 manj^ examples to prove the contagiousness of the so-called hog-cholera. 



The mycotic theory, which is now so popular among scientific men, and 

 which ascribes the disease to parasites of the lowest form and smallest 

 size, would seemingly offer the only explanation for this disease. It can- 

 not be a toxic poison, as no one has ever been able to demonstrate an 

 organized ])oison as a cause of any contagious disease. The lowest forms 

 of organisms live in the air and in water as well as when attached to solid 

 bodies. A specific germ, a favorable medium of develoi^ment, and con- 

 tact with the animal to be infected are fundamental conditions for the 

 development of the disease and its diffusion ; and every purturbation, 

 every solution of continuitj^ in the chain of these factors of developinent 

 may prevent Or lessen its destructive action. 



From numerous observations I am convinced that the moving of dead 

 animals does not import the disease as readily as do the live ones. I am 

 led to beUeve that putrefaction diminishes the capacity for infection, and 

 that the bacteria of decomposition is destructive to the germs of the dis- 

 ease. It is a well-known fact that one low form of organism is destruc- 

 tive to another low form. Climatic influences have but little control. I 

 think that warm weather acts more favorably to the formation of the 

 infecting germ. Along belts of timber it readily spreads ; it also ex- 

 tends out on the prairie where the growth of vegetation is luxiulant. 

 Contact of diseased with well animals imports it under all circumstances, 

 climate having no influence to prevent its spread. As to diet and care, 

 it matters not how well or how poorly fed, or how cleanly kept, if sucb 

 well-fed hogs come in contact with the disease, they are as sure to con- 

 tract it as those that have no care. Where not caused by other means, 

 the prevailing wind gives the direction or march of the disease. The 

 greatest distance that it has 'peon carried by the wind, iu any well-au- 

 thenticated case that has come under my observation, is two miles. As 

 a rtile, a greater or less niunber of animals in every herd will escape the 

 disease, or have it so lightly as not to interfere with their doing well. 



It appears that quantity as well as quality of the germ, and aptitude 

 of the unimal to receive it, are the conditions which influence contagion. 

 Some animals possess an absolute power of resistance. Trousseau says 

 that "there are individuals Y*'ho pass unharmed through every kind of 

 an epidemic, be it influenza or cholera, scarlet fever or measles, small- 

 pox or typhoid fever. There are indi\i.duals whom it is impossible to 

 affect with the vacciae virus ; inoculate them twenty times, and j'ou will 

 obtain no result. If I may use the expression, 'the soil is barren,' a.nd 

 in it the seed cannot germinate. There are others again in whom the 

 l)Ower of resistance is oiHy temporary. It is in general difficult to find 

 out the condition upon which this power of resistance depends. It is 

 known that the ability to resist contagion varies -with the age of the in- 

 dividual. There is less power of resistance in the youth than in the old 

 man. One attack of a contagious disease generally confers complete 

 immunity from any subsequent contamination. Occasionally it may be 

 repeated, but these exceptional cases do not at all invalidate the general 

 rule." 



The same writer still further says : " It would appear that virus or 

 morbific matter, iq)on its entering the economy ibr the first time, puts in 

 motion all therein that is fermentable, and so thoroughly destroys it 

 that the leaven — the contagion — when introduced again, finds nothing 

 whereupon to exert its action." 



Wilson says : "That in every epidemic there is always a great variety 

 in the gravity of the disease, some cases being very serious, others very 



