Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/734

Rh 676 NUTRITION fat which should be absorbed in the alimentary canal remains in part in the faeces, which acquire a peculiar putrescent odour. Pancreatic Juice. It we except the gastric juice, the chemical action exerted by the pancreatic juice is the most potent and useful of any of the digestive secretions. When freshly secreted and perfectly normal, the pan creatic juice is a clear viscid liquid of strongly alkaline reaction and highly coagulable by heat. Its solid con stituents may reach the proportion of 10 per cent. It contains (1) water, (2) various albuminous bodies which cause the liquid to be coagulable by heat, and of which one is intimately connected, or indeed perhaps identical, with the ferment trypsin, (3) a number of ferments, (4) traces of products of digestion, as leucin and tyrosin, (5) salts. The ferments of the pancreatic juice are the following : (1) a proteolytic ferment termed trypsin, (2) a diastatic ferment, (3) a ferment which acts on fats, (4) a curdling ferment (1). The first-named ferment, unlike pepsin, which is quite inactive under this condition, acts most energetically in solutions which contain a free alkali or an alkaline carbon ate, although it possesses some action when the reaction is neutral or even faintly acid. Like pepsin, trypsin dis solves insoluble proteids and converts them into peptones ; it possesses, however, an activity which surpasses that of pepsin, inasmuch as it splits up certain of the peptones formed into simpler bodies, such as leucin, C 6 H 13 NO, and tyrosin, C 9 H 11 NO 3, the former of which is an organic body allied to the fatty acid group, and the latter to the aroma tic group. According to the views of Kiihne, the molecule of an albuminous or proteid body is capable of being broken up under the influences of such ferments as pepsin and trypsin into the allied bodies of smaller molecular weight, the peptones, which, though possessing general and common reactions, may by their behaviour towards certain chemical agents as well as towards ferments be sub divided into two groups, a 7^a -group and an anti-group. Kiihne believes that both pepsin and trypsin decompose the proteids with the production of so-called hemi-peptones .and anti-peptones, and that, whilst neither pepsin nor trypsin can further decompose anti-peptones, trypsin possesses the power of splitting up hemi-peptones into simpler bodies. The amylolytic or diastatic ferment of the pancreatic juice resembles that of the saliva in its action. Whilst the saliva of most animals contains no such ferment, the pancreatic juice of all animals is very rich in diastatic ferment, so that the action of the pancreatic juice on starch is much greater than that of saliva. The fat-decomposing ferment sometimes, though errone ously, called the &quot; emulsifying ferment &quot; of the pancreas is present in exceedingly small quantity and is very readily destroyed, so that its existence has sometimes, though erroneously, been denied. It breaks up the neutral fats in part into their respective fatty acids and glycerin. This slight acidification unquestionably facilitates the formation of an emulsion of the remaining fats. All these ferments are influenced by temperature in nearly the same manner as the ferments of saliva and gastric juice. Boiling destroys them absolutely, cold retards their activity, the body temperature is very favour able to them. The most suitable medium for them is the alkaline juice in which they occur, and the alkalinity of which is due to sodium carbonate. The following is an analysis of the pancreatic juice of the dog : Water (in 1000 parts) 900 8 Solids 99 2 Organic matters 90 - 4 Inorganic matters... 8 8 Intestinal Juice. This juice, which is also called not unfrequently by its Latin name succus entericus, is a thin, yellowish, alkaline, albuminous liquid of specific gravity I Ol, concerning which we possess very little certain in formation. It has been said to act upon fibrin alone of the albuminous bodies ; it not only contains a small quantity of a diastatic ferment but probably also a so- called inverting ferment, possessing the power of converting cane-sugar into grape-sugar. Fate of Food- Stuffs in the Alimentary Canal. The food which is introduced into the mouth is an exceedingly complex substance. Leaving out of account those sub stances which are insoluble and incapable of absorption, and which are also not amenable to the influences of the digestive juices, we may classify the true food-stuffs as follows. (1) Albuminous matters, including (a) the true proteids, such as albumen of egg, casein of milk, myosin of muscle, fibrin of blood, &c. , and (b) the albuminoid bodies, such ns gelatin from tendons and bones, chondrin from cartilages, and elastin from various elastic structures ; (2) hydrocarbons or fats, of which those chiefly used for food are stearin, olein, and palmitin ; (3) carbohydrates ; (4) the various itwrganic salts ; (5) water. The third group includes the amyloids or starch-like bodies, the saccharoses like cane-sugar, the glucoses like the grape-sugar and fruit-sugar found in honey and in ripe fruits, the sugar of milk, &c. In addition to these may be mentioned allied bodies, cellulose, pectin, arabin, mucilage, &c., which in some animals, or in some conditions, are certainly digest ible. In a subdivision of the same group we may place the various vegetable acids, lactic, acetic, citric, malic, &c., which are essentially foods. It may be premised that the fate which befalls a given example of ingested food does not depend solely upon the theoretical power of the digestive juices to act upon it. Thus digestible food may be imperfectly digested OAving to being passed into the stomach in lumps and masses, which the juices cannot permeate and the stomach cannot crush ; or starch may be so incorporated and en- capsuled with fat that the saliva and even the pancreatic juice may fail to reach it ; or digestion from one cause or another may be so prolonged that fermentative changes, to which most samples of food are inevitably liable from containing organized ferments or &quot; germs,&quot; may have time to begin and to alter materially the sequence of events. Hence we shall feel no surprise that much food escapes altogether the action of digestion. The most perfect and economical feeding is that in which the least quantity of food is passed through the alimentary canal unchanged. When, however, the just quantity is taken, and the digest ive organs are sound, the following is the order of the changes which occur. Food placed in the mouth at once excites the flow of mixed saliva and mucus. Solid food is broken up, rubbed together with the juices of the mouth and entangled air-bubbles, and rolled into a slimy bolus. Soluble con stituents of it thus have an opportunity of becoming dis solved at once ; sugar, dextrin, vegetable acids, and many inorganic salts would, in part at least, pass into solution in the mixed saliva. The process of mastication, besides triturating the food and mixing it with the alkaline saliva, permits it to become raised nearly to the body-temperature, in which condition the dextrin and the starches readily fall a prey to the ptyalin, and begin to be converted into dextrins and maltose. This change is very rapidly effected it begins instantly if the starch is already boiled ; so that, unless the food is &quot;bolted,&quot; a considerable quantity of soluble dextrin and sugar is formed before the bolus is swallowed. The act of deglutition passes the softened bolus into the stomach, where already a certain quantity of acid gastric juice is ready to receive it. The presence of food in the stomach is a greater stimulus to the gastric flow than its presence in the mouth : the juice is more rapidly secreted, but still it is comparatively poor in pepsin