2/38 The best known example of this is in the highly infectious disease of swine known as hog cholera. It has been shown that in this disease two organisms are associated,--one an invisible and filterable organism, and the other a bacillus. It was first supposed that the bacillus was the specific organism; it was found in the lesions and certain, but not all, the features of the disease were produced by inoculating hogs with pure cultures. The disease so produced is not contagious, and the contagious element seems to be due to the filterable virus. In the preceding chapter we have seen that in the infected individual the disease extends from one part of the body to another. |