654 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



lire liq-aid, either once or twice, left the animal as susceptible to nat- 

 ural infection as before inoculation, and in a few cases produced a 

 virulent typo of the disease. We have already dwelt upon the im- 

 portant fact that the disease can be producc^l by feeding when sub- 

 cutaneous inoculation fails. This may also explain the failure of 

 protective iuoorjlation. The disease exerts its severest effects locally 

 upon the mucosa of the large intestine, and in only a few cases is it 

 a real septicaemia. The bacteria have the power of rapid m-ultipli- 

 cation within the vascular system only when exceptionally virulent. 

 Subcutaneous inoculations of cultures, in which they may have be- 

 come attenuated, are of little avail, because they are speedily destroyed 

 in the connective tissue, leaving only a slight local swelling behind. 

 Other lines of investigation must therefore be followed out before 

 any j)ractical results can be obtained. 



HOW CAN HOG-CHOLERA BE PREVENTED ? 



The measures which must be adopted to prevent the introduction 

 and spread of hog-cholera depend upon our knowledge of the disease 

 as it appears in herds, and more especially upon a study of the cause. 

 This we have demonstrated to be a microscopic plant organism be- 

 longing to the class of bacteria, and res'embling in a general way those 

 organisms which are the cause of infectious diseases among men. 

 Of this disease the only reliable diagnostic lesion is ulceration of the 

 large intestine, or the presence of the bacterium in the body of the 

 affected animal, and whatever follows can only apply to the disease 

 produced by this specific organism or bacterium. 



It has been shown in this and preceding reports that the disease 

 spreads from one animal to another of the same herd until sometimes 

 only a small percentage of unthrifty animals remain. It extends from 

 one herd to another, and may be carried long distances. The pres- 

 ence of the specific bacterium has been demonstrated in such widely 

 different regions as the District of Columbia, Illinois, and Nebraska. 



The fact that one animal takes the disease from another does not 

 explain how the virus is transferred. Is it carried directly from one 

 to another in the air, or is it deposited in the soil by one animal to 

 be taken up by another? Is it introduced through a wound in the 

 skin? Is it taken up by the lungs from the inspired air, or is it in- 

 troduced with the food and drink? These questions cannot be solved 

 by simply observing the disease in herds, hence numerous experi- 

 ments detailed in this and the preceding report have been directed 

 to a solution of these questions, upon which some rational rules for 

 prevention may be based. 



The disease is perhaps never communicated by injuries of the skin, 

 by bites and wounds obtained in other ways. Largo quantities of 

 liquid containing the virus can be introduced beneath the skin with- 

 out fatal results. In the great majority of pigs a local swelling is the 

 only effect. 



Whether the lungs serve commonly as an entrance to the virus 

 cannot bo definitely stated. All experimental evidence jDoints the 

 other way, and in a largo percentage of cases the lungs are intact, 

 while the large intestine is severely ulcerated. We have shown that 

 blood and tissue which have been dried for two months may contain 

 bacteria, which readily multiply when placed in proper media. Hence 

 the dust from pens where the disease exists may contain many bacte- 

 ria, which, on reaching the lungs, multiply and produce the disease. 



