=Overcoming abnormal fermentations.= The lactic acid bacteria are often looked upon as normal to milk, and it is certain that they are to be classed as harmful, only as they injure the keeping qualities of milk. In milk designed for butter and cheese their presence is necessary. At times these desirable forms of bacteria may disappear, and be replaced by less desirable types. In one case it was observed that the usual lactic bacteria had been replaced in a cheese factory supply by an acid-forming organism that produced an intensely bitter taste in the milk, thus rendering the cheese of no value. When such harmful forms appear, they must be overcome, and the normal types of bacteria replaced. A thorough cleaning of the milk utensils, attention to the cattle and all places from which such bacteria may find their way into the milk is often sufficient to cause a disappearance of the trouble. If the acid-forming bacteria have disappeared, the inoculation of the milk with cultures in ways later to be discussed is often of advantage. At times more stringent measures must be employed in order to destroy the harmful bacteria, such as the use of strong disinfectants. =Disinfection and disinfectants.= If any building or room becomes infected with disease-producing bacteria, or if organisms causing abnormal fermentations become established in a factory, the use of a disinfectant that will destroy with great rapidity the life of bacteria is necessary. The disinfection of all types of dairy apparatus and utensils can be accomplished by thorough cleansing, and by the use of steam or boiling water. The disinfection of rooms and stables cannot be so readily accomplished. Consideration must always be given to the resistance of the organism it is desired to destroy. Those that form spores are very resistant toward all chemical agents, while those that do not produce these resistant bodies are easily killed. In the dairy and factory, it is often necessary to destroy the organisms that develop in decomposing organic matter. Here, as in all disinfection, a thorough cleaning should precede the application of any disinfectant. Some chemicals act as deodorants, _i.e._, destroy the offensive odor, without removing the cause. It is impossible effectually to destroy bacteria embedded in a mass of organic matter, and through the removal of the material itself, the larger part of the bacteria will be removed. The disinfectant then comes in direct contact with the surface to be disinfected, consequently destroys the bacteria not removed in the cleaning. All places in which dairy work of any kind is done should be provided with an abundance of light and air. The direct rays of the sun have a powerful disinfecting action, and light makes evident accumulations of dirt that in a darker room would be unnoticed. Ventilation keeps the rooms dry and thus prevents the growth of mold and the development of a musty odor.