SO masterly and complete was the account which Koch gave in 1884 of the comma-bacillus, which he held to be the virus of cholera, that but little, if anything, has been added to our knowledge of its mode of growth, of its reaction to dyes, or of its life-history. As might be expected, the assiduity of many observers, now it has been directed to the subject, has led to the discovery of many other bacilli, which may be described as comma-shaped. But, so far, no bacteriologist, who has had his observations corroborated by other observers, has proved that any of them are indistinguishable in all their physical characters, whether in appearance, in reaction to dyes, or in their mode of growth, &c., from the choleraic bacillus. So far as is known, animals are rot susceptible to cholera. If Asiatic cholera could be induced by inoculating with pure cultivations of choleraic comma-bacilli, then beyond a doubt they would be the vera causa, or, in other words, the contagium of cholera; but this step in Koch's argument was wanting, probably for the above-named reason, and is likely to remain so the experimental inoculations of guinea-pigs which have taken place being by no means conclusive.