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And this element possesses the remarkable power of converting starch into sugar, which is the first step in its digestion. Though many azotized substances in a state of decomposition exert a similar agency, yet it is possessed by ptyalin in a much greater degree. The gastric juice has probably no action on farinaceous substances.
This enables the ptyalin of the saliva to continue its action for a longer time than if the starch were eaten first. *Liquids during the Meal.*—Liquids as ordinarily taken during the meal are objectionable. They tend to diminish the secretion of the saliva and to cause rapid eating.
The ptyalin starts starch digestion, but it does not work in the presence of acid. Eating acid fruits makes the mouth acid temporarily, and consequently the starch does not receive the benefit it should from mouth digestion. The result is an increased liability to fermentation in the alimentary tract. To get the best results it is absolutely necessary to masticate all starchy foods well.
Digestive enzymes perform relatively simple functions breaking large molecules into smaller parts that can dissolve in water. Digestion starts in the mouth when food is mixed with ptyalin, an enzyme secreted by the salivary glands. Pylatin converts insoluble starches into simple sugars.
We are not certain that nicotin ruins ptyalin; we are certain that the functions of other organs are vicarious of those of the salivary glands. We say that it is not satisfactorily proved that tobacco impairs the sugar-making function of the saliva. At least, we have never seen the proof from recorded experiments.
A and B give no evidence of sugar, while C reduces the Fehling, giving a yellow or red deposit of cuprous oxide. Therefore, starch is converted into a reducing sugar by the saliva. This is done by the ferment ptyalin contained in saliva. The Pharynx and OEsophagus. The dilated upper part of the alimentary canal is called the pharynx. It forms a blind sac above the level of the mouth.
Those who eat in moderation may eat starch and flesh in the same meal without getting into trouble. In winter it is all right to take starch with the sweet fruits. It is best to avoid mixing acid fruits and cereals. Even healthy people find that a breakfast of oranges and bread does not agree as well as one of milk and bread. The saliva, which contains ptyalin, is secreted in the mouth.
A babe's salivary glands, until he be six or seven months old, does not secrete its proper fluid namely, ptyalin, and consequently the starch of the farinaceous food and all farinaceous food contains starch is not converted into dextrine and grape-sugar, and is, therefore, perfectly indigestible and useless nay, injurious to an infant, and may bring on pain and convulsions, and even death, hence, the giving of farinaceous food, until a child be six or seven months old, is one and the principal cause of the frightful infant mortality at the present time existing in England, and which is a disgrace to any civilized land!
It acts with vigor on all of the nutrients insoluble in water, producing the following changes: 1. It converts the starch into maltose, completing the work begun by the saliva. This action is due to the amylopsin, which is similar to ptyalin but is more vigorous. It changes proteids into peptones and proteoses, completing the work begun by the gastric juice.
Now, this starch must be converted into glucose before the system can appropriate it, and as exhaustive experiments have shown that not more than four per cent. of the starch is converted by the ptyalin in the saliva, the principal work of dealing with the starch devolves upon the duodenum, or second stomach, the fluids of the main stomach having no action upon it.
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