REPORT OF THE BUKEAU OF ANIMAL INDUSTRY. 135 



such, a nidus, although, the peculiar hepatization is not originally due 

 to swine plague. 



In the cases of swine plague, pleuritis was a common and promi- 

 nent lesion, directly traceable to the virus. It is not unlikely that pleu- 

 ritis in old cases of hog cholera is caused now and then by septic or- 

 ganisms entering the serous cavities through the ulcerations in the 

 large intestines. 



It is interesting to note the uniformity with which ulceration of the 

 large intestine accompanied intra-abdominal injection of hog cholera 

 bacilli in the vaccination experiment. The superficial character of 

 most of the ulcerations would lead us to assume that the virus had 

 acted upon the mucous membrane from the surface rather than in the 

 form of emboli from the sub-mucosa, in which case we should expect 

 the ulcers to be deep and rather small in size. There was no evidence, 

 except in one case (No. 484), of injury to the wall, and we may have 

 to accept the alternative that only two or three animals were inocu- 

 lated with insufficiently sterilized cultures, and that the remainder 

 took the disease from these by taking the virus in with the food. 



The experiment of intra-abdominal injection of sterilized cultures 

 in large quantities has since been repeated without any accident, and 

 will be reported when completed. 



INVESTIGATIONS OF SWINE DISEASES IN IOWA. 



In determining upon rules and regulations necessary for the sup- 

 pression and prevention of infectious diseases it is necessary to know 

 their causes aiid all that pertains to their life history. As long as 

 these are not fully known the rules that are laid down can only be 

 regarded as provisional and subject to change after more thorough 

 investigations. For the same reason the preventive measures appli- 

 cable to one disease can not be applied to another if there are differ- 

 ences in the microbes -that cause the diseases. We have already 

 demonstrated in this and former reports that all infectious swine 

 diseases in our country are not the same. A We have separated them 

 into two diseases, hog cholera and swine plague. Although there is 

 much that is alike in both diseases and in the bacteria causing them, 

 the latter are distinguished from one another in a number of ways, 

 the most important of which is a difference in their resistance to de- 

 struction and their behavior in the surroundings of the animals, such 

 as soil, water, etc. 



One of the problems before us now is to determine the relative dis- 

 tribution of these two diseases in our country. Are there certain 

 regions overrun by one of these diseases and free from the other ? 

 What regions are afflicted with both diseases ? 



It was to aid in solving these questions that advantage was taken 

 of the reported prevalence of swine disease about Mason City, Iowa, 

 in November, 1888. Owing to the very willing assistance of Messrs. 

 L. M. Van Auken, H". I. Smith, and others, of Mason City, in locat- 

 ing for us the places where the disease existed, and in furnishing 

 valuable information concerning the spread of disease in that section 

 of the country, as well as the readiness with which the owners of 

 diseased swine placed all the means and animals at our disposal, it 

 was possible to examine several animals from three separate farms 

 within two days. Owing to the exigencies of bacteriological work 

 it is necessary to work quickly in order to obtain any results. 



Farm A. The disease appeared about November 1, in a herd of 



