The character of the milk is greatly influenced by the environment in which the cow lives. The stable in which the cow is kept should be clean, well ventilated, and protected against extreme changes in temperature, thus being cooler in the summer than the hot air on the outside and much warmer in the winter. An excellent arrangement of the stables to secure cleanliness and good ventilation is shown in Fig. 13. Cows should be supplied with an abundant quantity of pure water and should not be allowed access to stagnant pools when pasturing in the summer. Every animal giving milk should be examined from time to time by a competent veterinarian to determine, by the injection of serum or otherwise, whether or not the animal is afflicted with tuberculosis. Every animal infected with tuberculosis should be separated from the herd and destroyed. Tuberculosis is an infectious disease and may spread from a single cow to every one in the herd. It is still by some authorities claimed that there is no authentic case of transmission of bovine tuberculosis to the human system. Other authorities hold that such transmission is possible, even if it has not been proven in a particular case. Since experts disagree on this point the same rule is applicable here as in other cases of the same kind, namely, where experts disagree on a point relating to the public health the benefit of the doubt, if any, should be given to the public, and the advice of those experts followed which is the most radical respecting the protection of health from infection of any kind. It would be difficult to prove, for example, in any case of tuberculosis in man that it had been contracted from the sputa of tuberculosed patients, yet because it is possible, in the opinion of many experts, that such infection and transmission of disease can take place, it is the part of wisdom to guard against it.