The conditions which permit peptic digestion to take place are, therefore, precisely those which exclude the action of saliva." He sees no reason, however, why we should eat foods requiring salivary digestion at meals separate from those at which we eat foods requiring peptic digestion. Indeed, he declares of the salivary enzyme, ptyalin, "the enzyme is extremely sensitive to acid. Inasmuch as the gastric juice is decidedly acid it used to be claimed that salivary digestion could not proceed in the stomach. But it has come to be recognized that when a large mass of food is introduced into the stomach within a short time the gastric juice penetrates it rather slowly. A few minutes after the completion of a meal we may picture the stomach contents as being acidified near the surface, the acid slowly making its way inward, but having a neutral or even alkaline central portion. Salivary digestion will be continued in the steadily diminishing region not yet reached by the acid, and will cease only when the gastric secretion from one wall of the stomach meets that from the other."

This effort to escape the practical application of the physiological limitations of the digestive enzymes might have some merit, if we were in the habit of swallowing our food en mass, and not small amounts at a time. At the same time, the alkaline saliva must impede the work of pepsin, a thing that would be reduced to a minimum if proteins, which require little insalivation, were eaten alone. (It is not true that gastric juice is decidedly acid. It is sometimes strongly acid, sometimes very weakly acid, depending upon the character of food eaten). Why spend years in the study of physiology if we are to forget it immediately and disregard the practical applications that may be made of our knowledge of physiology.

Milo Hastings objects that laboratory feeding experiments have disregarded food combinations and have given attention to the diet as a whole. This objection has little weight. It is quite obvious that the laboratory has not given us the last word on feeding and Mr. Hastings is in no position to say that if and when combinations are tested in the laboratory the experimenters will not obtain better results than now in their feeding experiments.

Certainly foods requiring an alkaline condition for their digestion should not be eaten with foods necessitating an acid condition for their digestion. Foods requiring an alkaline condition for digestion should not be eaten with acids.

Stiles continues: "Any rotation of the contents would probably bring about an earlier distribution of the acid and arrest of starch digestion. No such rotation seems normally to occur." While there may be no rotation of the contents of the stomach, there is certainly considerable movement in it and this serves, as Stiles himself bears witness, to mix the semi-fluid foods. He talks of the food in the stomach as though it were more or less a solid mass through which the digestive juices must pass by osmosis; whereas this mass of chewed food, food juices, saliva and usually water, is a semi-fluid mass in constant to-and-fro motion. Assuming that he is right, there would still be interference with salivary digestion in those starches on the outside of the food-mass.

V. H. Mottram, professor of physiology in the University of London, says in his Physiology that it is in the distal end of the stomach that the churning movement mixes the food and gastric juice and no salivary action is possible. Now gastric juice digests protein and saliva digests starch. Therefore, it is obvious that for efficient digestion the meat (protein) part of a meal should come first and the starchy part second--just indeed as by instinct is usually the case. Meat precedes pudding the most economical course of procedure."

Mottram at least recognizes the fact that an acid gastric juice destroys ptyalin and stops starch digestion, even if he tries to squirm out of any rational application of the fact. Instinctively, as observed in the eating habits of wild animals (and of domestic animals also, where they are permitted to choose their own foods) proteins and carbohydrates are eaten at separate meals, not protein first and starch last. It is customary to eat meat, eggs, cheese, etc., and bread together. Watch a man eating a hamburger and see if he is instinctively taking his meat at the first part of his meal and his starch last. We can only assume that Prof. Mottram does not want to be classed as a "faddist," else he would not have resorted to this obvious "dodge" to escape the logical application of the facts of digestive chemistry he had presented.

Tilden, who was once a professor of physiology in a medical college, remarked: "Educated (scientific) M. D.'s, have known all about the chemistry of digestion, because their bosom companions, the Ph. D.'s, have overworked their laboratories, and particularly their glass stomachs (the immortal test-tubes), to serve their doctor friends." It is unfortunate that the physiologists have been so anxious to justify conventional eating practices and so unwilling to make any practical applications of the factors of digestive chemistry in eating. Had the physiologists not been derelict of their duty, our eating practices of today might be far different.

One objection to this rule of food combining often made is that the stomach is always acid. This assertion is made in obvious disregard for the facts of digestive chemistry which we have already learned. We know that the type of juice that is poured into the stomach is determined by the kind of food that is eaten.

Perhaps the most common objection made to this rule is that Nature, herself, has produced protein-starch combinations. Indeed, it is often asserted that almost all natural foods are starch-protein combinations. Alfred W. McCann reasoned that if nature combines starches and proteins in the same food there can be no harm in us combining them in the same meal. Carlton Fredericks, a biochemist, makes a somewhat similar objection to this rule. Such objections are made in obvious ignorance of the facts of digestive adaptations. The objectors should study physiology a little.

There is a marked difference between the digestion of a food and the digestion of a mixture of different foods. Let us look at the digestion of bread: here we have an almost neutral gastric juice while starch digestion is going on and, then, after starch digestion has been completed, a highly acid gastric juice is secreted to digest the protein.

Pavlov proved another thing with regard to the purposive adaptation of the digestive juices. Bread proteid requires much pepsin and but little acid. This requirement is met, not by an increased flow of juice, but by an extraordinary concentration of the juice secreted. Acid inhibits the digestion of the starch of the bread and so an excess of hydrochloric acid is avoided. It is obvious, from these facts, that the eating of a bread and meat combination is exceedingly unphysiological. Yet this simple practical application of our knowledge of the complex process of digestion is constantly ignored.

If wheat is eaten alone (a monotrophic meal), there will be secreted a juice poor in hydrochloric acid but rich in pepsin. This juice will be poured out over a long period of time. Thus starch digestion and protein digestion go on concurrently. If meat and bread are eaten together much hydrochloric acid is poured out, so that starch digestion is suspended. If we eat but one food at a meal, nature can adapt her digestive juices to the food; but if we are going to eat several foods at a meal, this adaptation is impossible, unless the food is properly combined. At that, cereals and pulses, which represent protein-starch combinations, sweet potatoes, a sugar-starch combination and sour apples, an acid-starch combination, are prone to produce fermentation.

Dr. Richard C. Cabot, of Harvard, says: "When we eat carbohydrates the stomach secretes an appropriate juice, a gastric juice of different composition from that which it secretes if it finds proteins coming down. It is one of the numerous examples of choice or intelligent guidance carried on by parts of the body which are ordinarily thought of as unconscious and having no soul or choice of their own."

This statement of Cabot's presents a fact of physiology. It is borne out by Pavlov's showing that each kind of food calls forth a particular activity of the digestive glands. The digestion of starches and proteins is so different that when these foods are eaten together, they interfere with the digestion of each other. The acid poured into the stomach to digest the protein prevents starch digestion.

To a single article of food that is a starch-protein combination the body can adjust its juices, both as to strength and timing, to the digestive requirements of the food. But when two foods are eaten with different, even opposite, digestive needs, this precise adaptation of juices to requirements becomes impossible. If bread and flesh are eaten together, instead of an almost neutral gastric juice being poured into the stomach during the first two hours of digestion, a highly acid juice will be poured out immediately and starch digestion comes to an almost abrupt end. (Please note that carnivores in nature never mix carbohydrates with their meat.) Thus it is apparent that Frederick's statement that "the body is equipped to handle carbohydrates and proteins simultaneously with great efficiency" is not accurate and is based on ignorance of the facts of physiology.

It is true that the natural combinations offer but little difficulty in digestion, but neither the food factories nor the cooks have been able to produce protein-starch combinations capable of digestive completion. What nature has combined, nature can digest. What man may combine, she often finds indigestible. Dr. Tilden was eternally right when he repeated on more than one occasion that nature never produced a sandwich.