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468 lus. Therefore, it has been advanced, as cholera can occur without the comma bacillus, the comma bacillus cannot be the cause of cholera. Against this it has been said that these observations were defective; that although the bacillus was not found, it by no means follows that the bacillus was not present at some time in the case.

4. The comma bacillus has been observed in the stools of individuals who did not at the time or afterwards suffer from cholera. To this it is answered that although one of the necessary conditions for the production of cholera was present, others, equally necessary, were absent. Possibly, as Pettenkofer remarked, for the production of an attack of cholera three things may be necessary, X, Y, and Z. The comma bacillus may be the X, but in the absence of the Y, certain local, and of the Z, certain personal conditions, disease does not result. 5. It has been found impossible by the administration of comma bacilli to produce in the lower animals true cholera, or any condition with clinical symptoms closely resembling cholera. Koch and others, in certain experiments on guineapigs, acting on the supposition that the acid in the stomach killed the bacillus, neutralized this by the administration of sodium carbonate, and paralysed the intestine by intraperitoneal injections of tincture of opium. In this way they claim to have succeeded in killing guineapigs with symptoms to a certain extent like those of cholera. There are many sources of fallacy in this experiment, as has been pointed out by Klein and others. Exactly similar results can be got by using the Finkler-Prior and other bacilli. The most promising experiments in this direction are those by Jablotny on the ground squirrel, Spermophilus guttatus. By administering to this animal comma cultures in alkaline media a disease in many respects like cholera was produced; and, in the intestines and discharges of the animals experimented on, cholera-like pathological changes were found, as well as comma bacilli. Variability of the cholera microbe.— Bacterio-logical studies, always difficult, are extremely so in