Food Dislikes.—Milk.—Nothing makes more clear the absolute dominion of the mind over the stomach than the likes and dislikes of people for various kinds of milk. Most Americans can take cow's milk with good relish, though there are a few to whom it is distasteful. In this country we have not had much experience with the milk of other animals. Even goat's milk is not commonly used. The very thought of taking it disturbs many people, and to take it with other food would almost surely produce disturbance of digestion. I have seen people while traveling quite upset over the discovery that goat's milk had been put into their tea or coffee. Mare's milk is commonly used in some parts of Europe and in many parts of Asia, but it would be quite impossible to most of our people. Sheep's milk is used in some places. Ass's milk is commonly used in parts of Asia and may be obtained in Spain and is said to be less likely to disagree with children in summer than cow's milk. Most American mothers would rather not hear of it.
The same thing is true of the milk products. Some people find certain kinds of cheese quite out of the question though other people relish them. It requires special training, not of stomach but of mind, to enable one to eat certain cheese, though once the habit has been acquired such articles are delicious. It is only in recent years that some forms of cheese with greenish tints have become popular in America. To serve them at a dinner a generation ago disgusted many people. Now a dinner does not seem complete without them.
The beverages of various countries illustrate this same principle. The wines the Spaniards care for are not palatable to the Italians, and vice versa. Beer, as the result of familiarity, is now drunk everywhere in Europe, but when it was first introduced into Italy from Germany, it was considered impossible to understand how anybody could take it and pretend that its taste was pleasant. The question is said to have been once asked of one of the Congregations at Rome whether it was permissible to take beer on fast days. The Cardinals who tasted it declared that not only did it seem to them permissible but that it was a mortification to drink it and therefore it was proper Lenten exercise.
Eggs.—Many people have a supposed natural repugnance for eggs which they are sure indicates that these are not good for them. As a result, the physician gets all sorts of stories with regard to the supposed effects of eggs. One person tells you that more than two eggs a day makes him bilious. Another will tell you that they are too heavy for him. A third will tell you that they are distinctly constipating. A fourth will tell you that they produce a tendency to diarrhea. Here, as with regard to milk, the experience of the tuberculosis sanatoria has shown that there are but few people who cannot, when properly persuaded and when eggs are given in various forms, take from four to six eggs in the day without injury, and even without inconvenience. In these cases, it is largely a matter of mental attitude towards the food. In many instances, it will be found that the disinclination began in some experience in childhood when an egg was not very good, or when it was served insufficiently cooked, or when, perhaps, eggs always cooked one way were made a staple of the diet for a considerable period. There are over one hundred [{247}] ways of cooking eggs and this variety of preparation will often make them palatable, and nearly always digestible.
Over and over again I have seen people who had thought that eggs made them bilious, and who accordingly had for long refused to eat them, put in circumstances (from tuberculosis, diabetes, or obesity) where eggs had to form a considerable portion of the diet. Then there was no difficulty about eating and digesting eggs. In three cases in my experience patients with an objection they thought constitutional, developed glycosuria, and then nearly all their desserts were custards, and eggs became a standing dish in their daily diet. In every case not only was there no trouble, but they got to like the eggs and wondered why they should ever have had any prejudice against them. Two of the patients were women, the third a man who had not touched eggs for many years. His wife's comment was: "Eggs always made him bilious when he did not take them, but now that he is taking them freely they no longer make him bilious."
Mental Changes and Digestion.—The change that has come over the public mind with regard to sour milk is a typical illustration of how much a difference in the mental attitude towards a food product may mean for its satisfactory consumption by many people. Sour milk, though many farmers and working people thought it a pleasant acid beverage, was for long looked upon as a product fit at most to be fed to the pigs, if, indeed, there might not be question even of the advisability of this. Only the very poor who craved the nutritious value there was in it, continued to take it to any extent. Even if the milk still tasted sweet, but broke when it went into the tea, that was enough to make it quite impossible for many sensitive stomachs.
Lactic Acid as a Bactericide.—Then came Metchnikoff's announcement that his studies showed sour milk to be an extremely valuable food material, but much more than that, an important auxiliary for the lessening of microbic life in the intestines. He seemed to be able to demonstrate that a great many bacteria, whose products, absorbed from the intestines, hastened that process of deterioration in the tissues that we call old age, were inhibited when sour milk or lactic acid bacteria were present. The general health of the person who took sour milk was, as a consequence, much better. Not only this, but processes of deterioration being lessened, prolonged life and even old age could be promised to those who drank sour milk in sufficient quantities. Metchnikoff had been brought to the study of this question by what he had seen on the Steppes of Russia. Among the nomad tribes a principal part of whose diet consists of soured mare's milk, he found a large proportion of very old people. In looking for the reason for this disproportionate longevity, he came to the conclusion that the sour milk had something to do with it. Then laboratory observations and experiments as to the influence of the bacillus, that causes the souring of the milk, on the growth of other bacteria, and especially such bacteria as are usually found in the human digestive tract, seemed to show that the lactic bacteria had a strong inhibitory effect on nearly all the pathologic flora of the intestines.
As the result of these studies, all the world is now quite willing to take its share of sour milk. We no longer hear the complaint that uncomfortable feelings in the digestive tract are the result of taking milk that was a little sour.
Since this doctrine of Metchnikoff's has come to be popularly known, fewer patients have insisted that they could not take milk in such quantities as the physician thought desirable for them. Before that, a persuasion with regard to the ease with which milk becomes contaminated with microbes, and the dread that it might thus be a source of disease, or at least of disturbance of digestion, made it very difficult of digestion for many people. Now that they have a good authority who insists that, even if it should become somewhat soured in the ordinary way, this, far from making it a pathological article of diet, rather adds to its value from a therapeutic standpoint, has changed the attitude of mind of these people.