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466 lation of a white mass of bacteria; at the top a scum of bacteria in various stages of degeneration. The cultures may die after five or six weeks. Agar is not liquefied, and in it the cultivations retain their vitality longer. On potato, at 20 to 30 C., the culture appears as a thin, brownish, porcelain-like film. In broth some of the bacilli form a scum on the surface ; others, falling in masses to the bottom, leave the body of the liquid clear.* Although, taken together and in conjunction with the morphological appearances, these culture characters are fairly distinctive, nevertheless certain other bacteria, such as Tinkler's spirillum, behave very similarly ; and, as the microscopic features of those other bacteria in some instances are very much like those of the cholera vibrio, a mistake is easily made. The production of what is known as " cholera red " by the addition of pure sulphuric acid to a culture in peptonized broth is also not quite distinctive of the cholera vibrio, for a similar reaction (indol reaction) is produced by some other bacilli.

In careful and practised hands the diagnosis of cholera by the microscopic and cultural characters of the vibrio may be made with practical certainty.

''Is the comma bacillus the germ of cholera? —''Although it may be safely asserted that cholera is intimately associated with the comma bacillus, it does not necessarily follow that this organism is the cause of cholera. Many attempts have been and are being made to establish such a relationship. Nevertheless, what may be considered as absolute proof is still wanting— such proofs as alone can be afforded by the production in man, or in the lower animals, of a disease in every respect like cholera by the administration of pure cultures of the comma bacillus. Short of this the proof may be said to be almost complete; indeed, by not a few the causal relationship of the bacillus to the disease is considered as established.