To the EditoT of the ANALYST. DRAB SIB,-It may interest the readers of the ANALYST t o how that mice seem to possess the power of distinguishing between oleomargarine and butter. The facts are these : Some time ago I received for analysis a lot of butters whose genuineness was questioned. The dishes in which the butters, preparatory to analysis, were melted, were, after the fat had been roughly poured off, permitted t o remain over night on one of my working tables. The next morning I was

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... sed to find that ten of the twelve dishes had been licked clean by mice, while two had been left untouched. My analyses finished, it turned out that all the suspected samples were pure butter with the exception of two, and, upon inspection, I discovered that these two were the very fats the mice refused to eat. It seemed hardly possible that this could be due to mere luck, so I spread out in a clock glass a lot of butter, and in another and similar glass a lot of oleomargarine. The glasses were placed along side each other on my table and allowed to remain over night. Next day I found the glass which had contained the butt,er polished as clean as though it had been well washed, whereas the one charged with oleomargarine was to all intents and purposes intact. The mice had merely nibbled at it. The result in this case was also conclusive. The mice dined on the two butters and completelyignored the oleos. The oleo in one gIass was untouched, and that in the other merely bore the footprints of a mouse. When no butter, but simply a glass of oleo was left on the table, the mice partook thereof, 'tis true, but only in small quantities. There is no doubt that a hungry mouse will eat oleo, but it seems that he will do so only on condition that there is no butter to be had. The fact is a curious one and shows what a keen capacity for discrimination a mouse possesses, I could not possibly have told previous to my analyses which fats were oleomargarine and which butter. How would it do to make this extraordinary acuteness on the part of mice the basis of a rough method for testing butter ? Methinks the wcxds " mouse test " would look and sound remarkably well. The mice could be kept in a cage, and the suspected fats temptingly displayed on watch-glasses arranged on a little shelf running from one end of the cage to theother. Perhaps some mice are incapable of making the distinction, and will eat oleo as greedily as pure butter. I have had no experience with mice other than with those which hang about my laboratory, consequently I am unable to say what would happen should a trial be instituted with a lot of outsiders. Here is a chance for original research ! Let those who have time, opportunity, and the requisite modicum of enthusiasm fall to. Perhaps there may be a future for the mouse test!-Yours, etc, L. W. MCCAY. I next set out four glasses, two containing butter and two oleomargarine.