This section is from the book "The Relation Of Food To Health And Premature Death", by Geo. H. Townsend, Felix J. Levy, Geo. Clinton Crandall. Also available from Amazon: Clean Food: A Seasonal Guide to Eating Close to the Source with More Than 200 Recipes for a Healthy and Sustainable You.
"There is no such case on record, although the pyloric end of the stomach, (i. e. the end on right side) has been cut out and the intestines sewed to the stomach. Such operations have seldom been successful, but it is probably due to the fact that they have never been made until the patient was almost dead of some malignant disease, such as cancer or ulcer."
"Until within a few years it was supposed that the gastric juice had no effect whatever upon the fats, but modern investigation has changed that view somewhat, and it is now understood that the gastric juice is capable of breaking down or disintegrating fat cells thereby setting the fat particles or globules free. This, no doubt, is a great aid to intestinal digestion. It is also believed that the fat is to some extent changed into fatty acids and glycerine by the gastric juice."
"'It converts cane sugar into grape sugar, thus preparing it for absorption into the system."
"Yes, cellulose."
"It is digested somewhere in the apparatus of the lower animals, but nowhere in man; in fact, it keeps starch from digesting, because starch is encased in small cellulose cells, and unless the cells are ruptured by cooking or by mastication, starchy cereals and vegetables are almost wholly indigestible."
"From one to four hours, frequently longer."
"Much depends on the kind of food, upon the cooking, and the mixture of different kinds of foods."
"Well, meat and tough vegetables, like peas and beans, require longer time for digestion than something that is easily dissolved, like the white of an egg. Then as to cooking, the longer meats are cooked, especially if roasted or fried, the harder and more insoluble they become, as heat coagulates, that is, makes the albumen in meat more solid."
"Yes, being saturated with fat, because the gastric juice of the stomach has only a limited effect on fat, and if eggs or lean meat be fried or saturated with it, the particles might aptly be termed encased, and could only be acted on to a limrted extent, if at all, by the digestive agents of the stomach. This is the reason why fried lean meat is so hard to digest."
"No, there are many other things. The fineness of the particles of food has much to do with it, and it will not require any labor to demonstrate that a particle, say the size of a pea or bean would not be so quickly dissolved, if it be dissolved at all, as a particle as small as very fine flour, so that the length of time food should require for digestion depends much upon how finely it is masticated or artificially divided, and this applies equally to both meats and starches. Another factor is the amount of acid in the stomach."
"Well, some persons secrete very little acid, and are almost wholly unable to digest meats; others have such strong acid secretions that they digest meats very quickly, but that very fact might in a measure prevent starchy foods from being dissolved by the saliva, so that the kind of food and the amount of acid in the stomach are both elements affecting the period of digestion."
"No; perhaps one of the most important of all is the demand of the system for food."
"Well, if the system has previously been supplied with more food than it can use, nature has some way of protecting herself by not adding to the burden already carried. Of course, if the intestines are loaded with matter and their action slow, the food would not be quickly drawn downward. It is believed that when the system is clogged or there is an excessive accumulation of matter in the bowels, that the stomach must necessarily be in sympathy, and it sometimes happens that roods remaining too long in the stomach and decaying there is the first symptom pointing to the fact that the digestive organs have been overloaded and that there is no demand for food."
"Some people say that the amount of drinks or fluid taken into the stomach has much to do with the duration of digestion."
"That is true. If the digestive juices are greatly diluted they must necessarily be much less active than if they have their full strength."
"It also influences digestion, from the fact that the temperature of the stomach must be maintained at about the normal heat of the body, If cold drinks be poured into the stomach, as a matter of course, digestion will be delayed until the stomach can be re-warmed."
"Yes, some people have very active stomachs but yet have inherited some antagonistic tendency to certain foods"
"Well, anything which affects the nervous system and in that way disturbs circulation, will affect digestion."
"It is because the stomach requires a large supply of blood, and if the blood from any cause is in excess in other organs the supply of the stomach will necessarily be diminished. Great mental excitement keeps the flow of blood to the head instead of the stomach, and the same may be said of every vigorous exercise. There is still another cause for the various periods required for digesting the different foods, that is, their chemical effect on each other. To illustrate, tea contains a large amount of tanic acid. If strong tea should be drunk after eating the white of eggs, the tanic acid of the tea would precipitate the albumen of the eggs and make it entirely indigestible. This is about the same process as that of tanning leather"
 
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