Page:Tropical Diseases.djvu/548

506 to. Flexner, Strong, Musgrave and others regard it as the cause of what they termed epidemic dysentery, in contradistinction to sporadic or endemic dysentery, which they regard as belonging to the pathogenic sphere of the pathogenic amœba. It is a rod-shaped bacillus with rounded ends, varying in size somewhat according to the culture medium, from 1 to 3 μ. in length by 0.4 to 0.5 μ in breadth. It closely resembles in its properties Bacillus typhosus, but differs in being non-motile and exhibiting active Brownian movement, and in the circumstance that some types of B. dysenteriœ display a more uniform generation of indol than does B. typhosus. After a brief preliminary acid production in milk, it gives rise to a gradually increasing alkalinization; it does not agglutinate in serum from typhoid cases, but reacts in serum from dysenteric cases to which B.typhosus does not respond (Flexner). Opinions differed at first as to the presence of flagella; it is now generally conceded that they are absent. It occurs in greatest abundance in dysenteric lesions and especially in the solitary lymphatic follicles of the large intestine, and in the mucus in the stools during the most acute stage of " epidemic " dysentery. It is pathogenic to many animals, but it does not produce in them, or only exceptionally, dysenteric lesions, although the toxins of the bacillus, pounded and killed cultures, when injected intravenously into rabbits and other animals, produce necrosis of the large intestine into which they are excreted by some selective action. One c.c. of the filtrate of freshly isolated dysentery cultures injected intraperitoneally is fatal to a rabbit. In two experiments on man, one intentional, the other accidental, ingestion of the pure cultures was followed, within a short time, by well-marked symptoms of dysentery. The bacillus agglutinates with the blood serum of " epidemic dysentery in dilutions of 1 in 10 to 200.* Further-