finding there a favourable condition for growth; some of them, however, live and grow for some time and are prominent agents in the changes by which butter becomes rancid. The butter maker is concerned with the ripening rather than with later processes. The object of the ripening of cream is to render it in a better condition for butter making. The butter maker has learned by long- experience that ripened cream churns more rapidly than sweet cream, and that he obtains a larger yield of butter therefrom. The great object of the ripening, however, is to develop in the butter the peculiar flavour and aroma which is characteristic of the highest product. Sweet cream butter lacks flavour and aroma, having indeed a taste almost identically the same as cream. Butter, however, that is made from ripened cream has a peculiar delicate flavour and aroma which is well known to lovers of butter, and which is developed during the ripening process. Bacteriologists have been able to explain with a considerable degree of accuracy the object of this ripening. The process is really a fermentation comparable to the fermentation that takes place in a brewer's malt. The growth of bacteria during the ripening produces chemical changes of a somewhat complicated character, and concerns each of the ingredients of the milk. The lactic-acid organisms affect the milk sugar and produce lactic acid; others act upon the fat, producing slight changes therein; while others act upon the casein and the albumens of the milk. As a result, various biproducts of decomposition arise, and it is these biproducts of decomposition that make the difference between the ripened and the unripened cream. They render it sour and curdle it, and they also produce the flavours and aromas that characterize it. Products of decomposition are generally looked upon as undesirable for food, and this is equally true of these products that arise in cream if the decomposition is allowed to continue long enough. If the ripening, instead of being stopped at the end of a day or two, is allowed to continue several days, the cream becomes decayed and the butter made therefrom is decidedly offensive. But under the conditions of ordinary ripening, when the process is stopped at the right moment, the decomposition products are pleasant rather than unpleasant, and the flavours and aromas which they impart to the cream and to the subsequent butter are those that are desired. It is these decomposition products that give the peculiar character to a high quality of butter, and this peculiar quality is a matter that determines the price which the butter maker can obtain for his product.