Odors of these two classes, due to volatile compounds in the milk, are of most importance in the milk and cream trade, as the faults largely disappear in making butter and cheese. Thorough æration is often helpful in the removal of such flavors. Odors of the third class, except in some very rare cases where the udder itself is the seat of colonies of bacteria, are not observed in freshly-drawn milk. The bacteria, molds and yeasts which cause them must have a chance to develop and to set up chemical changes in the milk; and this rarely occurs to any great extent within 12 hours from the time the milk is drawn. A high temperature, however, is favorable to growth of these low forms of plant life; so in warm weather milk faults are common. In butter-making, and in cheese-making, also, the heat often used to ripen the cream and the high temperature at which the milk is held in “setting” and “cooking” the curd, furnish conditions very favorable to the germs present and they develop with great rapidity. In their growth part of the milk is used for food and in its breaking down into simpler compounds the aromatic substances which make flavor, good or bad, are formed. The flavor of good milk and cream, then, is an inherent quality due to the normal constituents of the milk; the flavors of butter, both good and bad, except that due to the fat and to odors absorbed by the milk, are held to be the result of bacterial action; the fundamental flavors of cheese are probably due to chemical decomposition, started by unorganized ferments known as enzyms; joined with which are other flavors marking the individual cheeses, which are probably due to bacteria; and it has recently been found that in some cases yeasts have been the cause of bad flavor. FISHY FLAVOR IN MILK. [Sidenote: =Ready Relief.=] This peculiar smell, as though the milk had set in a close room with a barrel of not-too-fresh fish, was brought to the attention of the Bacteriologist by a dealer who had already located it as coming from the milk of a certain dairy. The dairyman is a more than ordinarily careful milk-handler, who gladly coöperated with the Station in efforts to locate the trouble in his herd. Bottles were supplied by the Bacteriologist, which had been steamed to insure the death of all germ life and then sealed. These sealed bottles were taken by the dairyman to his farm; at milking time each was opened long enough to receive a little milk from each quarter of the udder of a single cow; and then re-sealed. All were brought to the Station; and, upon examination, the odor was found only in the milk of one cow. The owner rejected her milk and heard no further complaint, from the dealer, of bad smells. This was the practical point; and it was thus easily and simply gained. [Sidenote: =Cause not found.=]