growth of micro-organisms, all of which phenomena suggest to us the action of bacteria.  Moreover, the flavours and the tastes that arise have a decided resemblance in many cases to the decomposition products of bacteria, strikingly so in Limburger cheese.  When we come to study the matter of cheese ripening carefully we learn beyond question that this a priori conclusion is correct.  The ripening of any cheese is dependent upon several different factors.  The method of preparation, the amount of water left in the curd, the temperature of ripening, and other miscellaneous factors connected with the mechanical process of cheese manufacture, affect its character.  But, in addition to all these factors, there is undoubtedly another one, and that is the number and the character of the bacteria that chance to be in the curd when the cheese is made.  While it is found that cheeses which are treated by different processes will ripen in a different manner, it is also found that two cheeses which have been made under similar conditions and treated in identically the same way 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