If the milk contains considerable numbers of yeasts, a sweet or fruity flavor is apt to develop, due to the products of the fermentation of the sugar by the yeast. This flavor resembles that of fermented fruit, or the bouquet of certain kinds of wine. =Putrid cheese.= In the absence of acid-forming bacteria, the cheese may develop a putrid or rotten odor, due to the growth of some types of putrefactive or digesting bacteria. This trouble is very infrequent in cheddar cheese, since this is made from ripened milk, but occurs more frequently in those types in which no acid is developed. Bacteria develop in the cheese in colonies or masses, just as they do in the plate cultures of the bacteriologist, made with transparent media, such as gelatin. Cheese is opaque; therefore, the growing colonies cannot be readily discovered, but when pigment-forming bacteria grow in the cheese, their presence is likely to be noted, because of the colored spots that are formed. =Rusty spot.= The "rusty spot" that has been encountered in New York and Canada is due to one of the colored bacteria which produces an orange or yellowish-red pigment. Various other pigment-forming organisms have been met in cheese, each producing its colored colony which differentiates itself from the mass of the cheese. If the pigment is produced in considerable quantities, and is soluble in any of the constituents of the cheese, the color will not appear in spots but will be more diffuse, or may impart a color to the entire mass. Cases of acute poisoning arising from the ingestion of cheese are not infrequently reported; similar instances result from the use of ice cream. In both cases it is believed that poisonous products have been formed by bacteria, probably by some of the putrefactive forms. From what has been said with reference to the abnormal fermentations of cheese, it will be seen that they are always due to the lack of acid-forming bacteria, or to their partial replacement by other types. In order to prevent such troubles, it is necessary to insure that the milk has been produced under clean conditions, from healthy cows, and has been handled in such a manner as to reach the maker in as sweet and fresh condition as possible. The maker can, by the use of proper starters, control the kinds of bacteria essential for the ripening process. A well trained maker should be able to prepare from such milk a uniform product of the highest quality. The effort of cheese makers at the present time is to handle milk of more or less objectionable quality so as to secure from it as good cheese as is possible. But cheese is so sensitive as to character of milk used that greater effort should be spent in securing an improved supply.