In the United States organisms, which culturally are mouse septicemia or swine erysipelas bacilli, have been isolated from the tonsils of five of sixteen pigs examined. These pigs all had hog-cholera, but it is probable that the bacilli were in the tonsils before they were infected with hog-cholera, and there is no evidence that they played any part in the disease. The distribution of the infection seemed to be restricted as most of the pigs from which the bacilli were obtained came from one litter. As we do not have clinical rotlauf, or swine erysipelas, in this country, as these organisms, in Europe, have been found in a large percentage of apparently normal swine, and as the disease is produced with difficulty by the injection of cultures, the question may be raised whether they are not secondary invaders rather than the primary cause of the disease with which they have been associated, or else whether the resistance of swine on the European continent does not differ from that of our breeds as a result of differences in foods.
It is possible that the mouse septicemia bacilli found in this country may differ culturally from those present in animals with swine erysipelas. With this in mind, the carbohydrate reactions, as well as other cultural characters not necessary for the identification of the bacilli isolated, have been studied.
The disease produced by the injection of these bacilli into mice and pigeons has been studied and shown to be largely an intracellular process. The organisms are taken up by the endothelial cells lining the veins and capillaries; there they multiply and soon kill the cells. It has also been shown that the only type of cell in the blood stream which contains bacteria is the endothelial leucocyte, and the probabilities are that the free phagocytes have been detached from the lining of the vessels. The disease is acute, and the indications are that in the cells the bacilli find a favorable medium for their growth. While phagocytosis may in general be an immune reaction, in this case it appears to favor the parasite rather than the host.