There were cases in which the lower segment of the small intestine, most marked immediately above the ileocaecal valve, extending thence upward, was of a dark reddish-brown color, the mucous membrane being covered with superficial haemorrhages.  In many cases the mucous membrane appeared to be superficially necrosed, and covered with diphtheritic patches.  The intestinal contents in such cases were not colorless, but consisted of a sanguinolent, ichorous, putrid fluid.  Other cases showed a gradual transition to a less marked change.  The redness was less intense, and was in patches, while in others the injection was limited to the margins of the follicular and Peyerian glands, giving an appearance which is quite peculiar to cholera.  In comparatively few cases were the changes so slight as to consist in a somewhat swollen and opaque condition of the superficial layers of the mucous membrane, with delicate rosy-red injection, and some prominence of the solitary follicles and Peyer’s patches.  In such cases the intestinal contents were colorless, but resembling meal-soup rather than rice-water.  In only a solitary instance were the contents watery and mucoid.  Microscopical examination of the intestine and its contents revealed, especially in the cases where the margins of Peyer’s patches were reddened, a considerable invasion of bacteria, occurring partly within the tubular glands, partly between the epithelium and basement membrane, and in some parts deeper still.  Then he found cases in which, besides bacteria of one definite and constant form, there were others also accumulated within and around the tubular glands, of various size, some short and thick, others very fine; and be soon concluded that he had to do here with a primary invasion of pathogenic bacilli, which, as it were, prepared the tissues for the entrance of the non-pathogenic forms, just as he had observed, in the necrotic, diphtheritic changes in the intestinal mucosa and in typhoid ulcers.

Passing to speak of the microscopical character of the contents of the bowel, Dr. Koch said that owing to the sanguinolent and putrescent character of these in the cases first examined, no conclusion was arrived at for some time.  Thus he found multitudes of bacteria of various kinds, rendering it impossible to distinguish any special forms, and it was not until he had examined two acute and uncomplicated cases, before haemorrhage had occurred, and where the evacuation had not decomposed, that he found more abundantly the kind of organism which had been seen so richly in the intestinal mucosa.  He then proceeded to describe the characters of this bacterium.  It is smaller than the tubercle bacillus, being only about half or at most two-thirds the size of the latter, but much more plump, thicker, and slightly curved.  As a rule, the curve is no more than that of a comma (,) but sometimes it assumes a semicircular shape, and he has seen it forming a double curve like an S, these two variations from the normal being suggestive