Besides its contents of internal secretions, valuable ferments, and mineral matters, milk must also be considered as an ideal form of nourishment owing to the fact that it contains all the necessary elements of human food. It is the most nourishing of all foods since it contains albumin, fat, and carbohydrates, the three main elements of human food, in large quantity. Good cows’ milk contains about 35 grammes of albumin, 40 grains of milk-sugar, and 35 to 40 grammes of fat to the liter. Thus if a person takes 2 liters of milk a day, or even less, 3 to 4 eggs, a little butter and several rolls, he can live comfortably without meat. We have made an experiment on ourselves by taking 1½ liters of milk, 4 eggs, 2 rolls, and 20 grammes butter a day as our only food, and after two weeks of such a diet, with a bodyweight of 68 kilos, we felt very well, and even lost no weight at the end of the trial. We have found in our own case, and in many patients, that with one plate of meat at dinner, together with vegetables and the above diet, with cheese, it is possible to live prosperously for months and to increase considerably in weight. The rosy cheeks of persons living on such a diet are the best proof of its efficiency. Those who do not like milk in large quantity may add a little cocoa, or a little weak coffee to it. For those whose stomachs cannot tolerate pure milk, a milk obtained by fermentation—kefir—is indicated. This can be prepared by fermenting cows’ milk with grains of kefir. It should not be fermented, for most purposes, for longer than one-half a day. By virtue of the carbonic acid which it contains it has a soothing action upon the walls of the stomach, and also promotes a better flow of gastric juice. Thus it is more easily digested than ordinary milk, whose valuable properties, however, it retains. Milk is also of value when taken in large quantity, since it checks the formation of bacterial and toxic products in the intestine, which, as we know, is enormously rich in such products, especially after having eaten animal food, like meat. milk-sugar and lactic acid are very powerful antiseptic substances probably the best natural intestinal antiseptics of which we know. This fact is made use of by Metschnikoff in the production of his lactobacilline, by which, through the formation of milk acid, the multiplication of the intestinal bacilli can be checked, and thus, according to Metschnikoff, old age prevented to some extent (see, also, Chapters XIX and XX). It is a very interesting fact that in countries where much of a certain kind of acid milk is used (e.g., Bulgarian “yogurth,” prepared with the aid of the Maya bacillus), there are many persons who live to be more than 100 (see Chapters VI and XIX). Some of the long-lived patriarchs whom we mention in this book, as Parr, who has lived to be over 152 years old, lived mainly on a milk diet.