Hog cholera is a very destructive disease and consequently of great economic importance. It is proving to be an important disease from the purely scientific point, as well because of recent significant discoveries in regard to its etiology. It is on this latter account that a gist of certain recent investigations, particularly by the Bureau of Animal Industry at Washington,1 under the direction of D. E. Salmon, is presented.
When the hog cholera bacillus (B. choleræ suis) was discovered, twenty years ago, it was believed that the etiology of this disease was solved. Facts were continually encountered, however, that did not harmonize with the generally accepted view that the disease is caused by the bacillus. A form of acute hog cholera in southwestern Iowa, in particular, presented high contagiousness, the blood of infected animals being virulent on subcutaneous injection into healthy, non-immune animals, and on recovery a definite immunity—