The custom of straining the milk in the barn has long been deprecated as inconsistent with proper dairy practice, and in the light of the above experiments, an additional reason is evident why this should not be done. Even after milk is thoroughly cooled, it may absorb odors as seen where the same is stored in a refrigerator with certain fruits, meats, fish, etc. ~Distinguishing bacterial from non-bacterial taints.~ In perfectly fresh milk, it is relatively easy to distinguish between taints caused by the growth of bacteria and those attributable to direct absorption. If the taint is evident at time of milking, it is in all probability due to character of feed consumed, or possibly to medicines. If, however, the intensity of the taint grows more pronounced as the milk becomes older, then it is probably due to living organisms, which require a certain period of incubation before their fermentative properties are most evident. Moreover, if the difficulty is of bacterial origin, it can be frequently transferred to another lot of milk (heated or sterilized is preferable) by inoculating same with some of the original milk. Not all abnormal fermentations are able though to compete with the lactic acid bacteria, and hence outbreaks of this sort soon die out by the re-establishment of more normal conditions. ~Treatment of directly absorbed taints.~ Much can be done to overcome taints of this nature by exercising greater care in regard to the feed of animals, and especially as to the time of feeding and milking. But with milk already tainted, it is often possible to materially improve its condition. Thorough aeration has been frequently recommended, but most satisfactory results have been obtained where a combined process of aeration and pasteurization was resorted to. Where the milk is used in making butter, the difficulty has been successfully met by washing the cream with twice its volume of hot water in which a little saltpeter has been dissolved (one teaspoonful per gallon), and then separating it again.[48] The treatment of abnormal conditions due to bacteria has been given already under the respective sources of infection, and is also still further amplified in following chapter. ~Aeration.~ It is a common belief that aeration is of great aid in improving the quality of milk, yet, when closely studied, no material improvement can be determined, either where the milk is made into butter or sold as milk. Dean in Canada and Storch in Denmark have both experimented on the influence of aeration in butter making, but with negative results. Marshall and Doane failed to observe any material improvement in keeping quality, but it is true that odors are eliminated from the milk during aeration. The infection of the milk during aeration often more than counterbalances the reputed advantage. Especially is this so if the aeration is carried out in an atmosphere that is not perfectly clean and pure.