may also ripen in a different manner, so that the resulting flavour will vary. The variations between cheeses thus made may be slight or they may be considerable, but variations certainly do occur. Every one knows the great difference in flavours of different cheeses, and these flavours are due in considerable measure to factors other than the simple mechanical process of making the cheese. The general similarity of the whole process to a bacterial fermentation leads us to believe at the outset that some of the differences in character are due to different kinds of bacteria that multiply in the cheese and produce decomposition therein. When the matter comes to be studied by bacteriology, the demonstration of this position becomes easy. That the ripening of cheese is due to growth of bacteria is very easily proved by manufacturing cheeses from milk which is deprived of bacteria. For instance, cheeses have been made from milk that has been either sterilized or pasteurized--which processes destroy most of the bacteria therein--and, treated otherwise in a normal manner, are set aside to ripen. These cheeses do NOT ripen, but remain for months with practically the same taste that they had originally. In other experiments the cheese has been treated with a small amount of disinfective, which is sufficient to prevent bacteria from growing, and again ripening is found to be absolutely prevented. Furthermore, if the cheese under ordinary conditions is studied during the ripening process, it is found that bacteria are growing during the whole time. These facts all taken together plainly prove that the ripening of cheese is a fermentation due to bacteria. It will be noticed, however, that the conditions in the cheese are not favourable for very rapid bacterial growth. It is true that there is plenty of food in the cheese for bacterial life, but the cheese is not very moist; it is extremely dense, being subjected in all cases to more or less pressure. The penetration of oxygen into the centre of the mass must be extremely slight. The density, the lack of a great amount of moisture, and the lack of oxygen furnish conditions in which bacteria will not grow very rapidly. The conditions are far less favourable than those of ripening cream, and the bacteria do not grow with anything like the rapidity that they grow in cream. Indeed, the growth of these organisms during the ripening is extremely slow compared to the possibilities of bacterial growth that we have already noticed. Nevertheless, the bacteria do multiply in the cheese, and as the ripening goes on they become more and more abundant, although the number fluctuates, rising and falling under different conditions.