7. After an animal has been fed for a long period on one kind of aliment, which, if continued, will not support life, allowing it the former customary food will not save it: he will eat eagerly, but will die as soon as if he had continued to be restricted to the article of food which was first given him.
Dr. Paris is of opinion that all that these experiments tend to prove is, that animals cannot exist upon highly-concentrated aliment. Horses fed on concentrated aliment are liable to various disorders, originating from diseased action of the stomach and liver, broken wind, staggers, blindness, &c.
Professor Muller has given an excellent definition of indigestion. “It is a state of the digestive organs in which either they do not secrete the fluid destined for the solution of the aliment, or they are in such a condition of irritability or atony, that by the mechanical irritation of the food, painful sensations and irregular motions are exerted.”
But the most curious experiments made on the changes which the food undergoes in the stomach, according to the greater or lesser facility with which it is digested, were those of Dr. Beaumont. This physiologist had the rare opportunity of investigating this subject in a patient of the name of St. Martin, who came under his care in consequence of a gun-shot wound, which left a considerable opening in the stomach, which, when empty, could be explored to the depth of five or six inches by artificial distention. The food and the drink could in this manner be seen to enter it. This enabled him to keep an interesting journal and table, showing the time required for the digestion of different kinds of food, which were taken with bread or vegetables, or both. The following are some of his interesting observations:
Experiment 33. At 1 o’clock St. Martin dined on roast beef, bread, and potatoes—in half an hour examined the contents of the stomach, found what he had eaten reduced to a mass resembling thick porridge. At 2 o’clock, nearly all chymified—a few distinct particles of food still to be seen. At half-past four, chymification complete. At 6 o’clock nothing in the stomach but a little gastric juice tinged with bile.
Ex. 42. At 8 a.m., breakfast of three hard-boiled eggs, pancakes, and coffee. At half-past eight, found a heterogenous mixture of the articles slightly digested. At a quarter-past ten, no part of breakfast could be seen.
Ex. 43. At 2 o’clock same day, dined on roast pig and vegetables. At 3 they were chymified; and at half-past four nothing remained but a little gastric juice.
Ex. 18, in a third series. At half-past eight a.m., two drams of fresh fried sausage, in a fine muslin bag, were suspended in the stomach of St. Martin, who immediately afterwards breakfasted on the same kind of sausage, and a piece of broiled mutton, wheaten bread, and a pint of coffee. At half-past eleven, stomach half empty, contents of bag about half diminished. At 2 o’clock p.m., stomach empty and clean, contents of bag all gone with the exception of fifteen grains, consisting of small pieces of cartilaginous and membranous fibres, and the spices of the sausage, which last weighed six grains.
As I have elsewhere observed, various are the theories that have been entertained in regard to digestion, but the experiments of Dr. Beaumont seem to have proved beyond a doubt, that this operation is due to the action of the gastric juice, with which he was enabled to produce artificial digestion. Having obtained one ounce of this solvent from the stomach of his patient, he put into it a solid piece of recently-boiled beef, weighing three drams, and placed the vessel that contained it in a water bath heated to 100°. In forty minutes digestion had commenced on the surface of the meat; in fifty minutes, the fluid was quite opake and cloudy, the external texture began to separate and become loose; in sixty minutes, chyme began to form. At 1 p.m. (two hours after the commencement of the experiment), the cellular substance was destroyed, the muscular fibres loose and floating about in fine small threads very tender and soft. In six hours they were nearly all digested—a few fibres only remaining. After the lapse of ten hours, every part of the meat was completely digested. The artificial digestion by these experiments appears to be but little slower than the natural process—they also demonstrate the influence of the temperature, and the quantity of the solvent secretion. Having obtained from St. Martin two ounces of gastric juice, he divided this quantity into two equal portions, and laid in each an equal quantity of masticated roast beef. One he placed in a water bath at the temperature of 99° Farh.—and left the other exposed to the open air at the temperature of 34°; a third similar portion of meat he kept in a phial, with an ounce of cold water. An hour after the commencement of the experiment, St. Martin had finished his breakfast, which consisted of the same meat with biscuit, butter, and coffee. Two hours after the meat had been put into the phial, the portion in the warm gastric juice was as far advanced in chymification as the food in the stomach; the meat in the cold gastric juice was less acted on, and that in the cold water only slightly macerated. In two hours and forty-five minutes from the time that the experiment was begun, the food in the stomach was completely digested, the stomach empty, while even at the end of six hours the meat in the gastric juice was only half digested. Dr. Beaumont, therefore, having procured 12 drams of fresh gastric juice, added now a portion to each of the phials containing meat and gastric juice, and to a portion of the half-digested food which he had withdrawn from the stomach two hours after the commencement of the experiment, and which had not advanced towards solution. After eight hours’ maceration, the portions of meat in the cold gastric juice, and in the cold water, were little changed, but, from the time of the addition of the fresh gastric juice, digestion went on rapidly in the other phials, which were kept at the proper heat, and at the end of 24 hours, the meat which had been withdrawn from the stomach after digestion had commenced, were, with the exception of a piece of meat that had not been masticated, converted into a thickish pulpy mass of a reddish-brown colour: the meat in the warm gastric juice was also digested, though less perfectly, while that in the cold gastric juice was scarcely more acted on than the meat in the water, which was merely macerated. Dr. Beaumont now exposed these two phials containing the meat in cold gastric juice, and meat in water, to the heat of the water bath for 24 hours, and the gastric juice, which when cold had no power on the meat, now digested it; while the meat in the water underwent no change, except that towards the end of the experiment, putrefaction had commenced. The antiseptic properties of the gastric juice were fully demonstrated in several other experiments.
Various philosophers, in idle disquisitions, have endeavoured by the most absurd hypotheses to determine what is the natural food of man, and to show that he is not created omnivorous. The comparison between our species and animals confutes these vain theories. The masticatory and digestive organization of man assigns to him an intermediate rank between carnivorous and herbivorous creatures. The teeth may be said by their figure and construction to bear a relation with our natural food. The teeth of flesh-eating animals rise in sharp prominences to seize and lacerate their prey, and those of the lower jaw shut within those of the superior one. The herbivorous animals are not armed with these formidable weapons, but have broad flat surfaces with intermixed plates of enamel, that they should wear less rapidly in the constant labour of grinding and triturating. In the carnivorous, the jaws can only move backward and forward; in the herbivorous their motion is lateral, as observed in the cow when chewing her cud. Beasts of prey tear and swallow their food in masses, while in others it undergoes a careful communition before it is transmitted to the stomach. The teeth of man only resemble those of carnivorous animals by their enamel being confined to their external surface, while in the freedom of the motion of the jaws from side to side they partake of the conformation of the herbivorous. The teeth and jaws of man are in all respects more similar to those of monkeys than any other animals; only in some of the simiæ the canine teeth are much longer and stronger, and denote a carnivorous propensity.