Imágenes de páginas
PDF
EPUB

174

Digestion more vigorous in Youth,

tious kind of food is a point of inferior consequence to the continually varying the nature of the aliment. Two principles are to be attended to in the regulation of diet; that the food be fit to furnish an abundant chyle, and that it duly stimulate the digestive organs. Every one has experienced the difficulty of continually varying the light and restricted diet of invalids, so as to find a grateful alternation of nutritive materials within the narrow limits allowed. In this instance the palate is a true guide to the wants of the stomach.

An adult person in health appears to require two hearty meals in the day; if subjected to much bodily exertion, a third repast becomes necessary, which otherwise seems to be superfluous. When the stomach is weakened by indisposition, more frequent meals of a lighter kind are requisite.

During infancy and childhood, when a large supply of materials is required to build up the enlarging frame, the appetite is proportionately more keen, the stomach appears to digest simple food more rapidly, and craves more frequent meals. It appears that protracted exertion and imperfect nourishment, if not continued for so long a period as to destroy the tone of the stomach, produce in adults a voracious digestion resembling that of childhood. The digestive organs are fitted by such abstinence for the active service required of them in providing materials for the restoration of the frame.

Mr. Hunter in illustration of this point makes the following extract from Admiral Byron's narrative, who, after describing the privations which he had suffered when shipwrecked on the west coast of South America, incidentally mentions their subsequent effect upon his

and after continued Abstinence.

175

appetite. "The governor," says Admiral Byron, "ordered a table to be spread for us with cold ham and fowls, which only we three sat down to; and in a short time dispatched more than ten men with common appetites would have done. It is amazing that our eating to that excess we had done, from the time we first came among these kind Indians had not killed us; as we were never satisfied, and used to take all opportunities for some months after, of filling our pockets when we were not seen, that we might get up two or three times in the night to cram ourselves *."

Nothing promotes hunger more than temperate exercise in fresh air; yet the appetite is never more vigorous than when a person accustomed to active habits is accidentally occupied for a day with sedentary pursuits. It seems that in the latter case the stomach employs besides its own power the energy which might have been expended in muscular exertion. On the other hand, if exercise unusually violent be taken so as to produce fatigue, the appetite is impaired. According to the theoretical language at present in use, the nervous energy has been in the latter instance disproportionately consumed on the muscular frame, and the stomach has received less than its due supply.

The habits of a literary life materially affect digestion; the neglect of bodily exercise, than which nothing more invigorates the system, and the derivation of nervous energy from other organs to the brains, contribute to impair the vigour of the stomach; at the same time the secretion of bile takes place more sparingly, and a hearty

[blocks in formation]

176 Digestion impaired by the Habits of a Literary Life.

meal finds every part of the alimentary system less capable of its office. The diet in such cases should be moderate, but not exactly simple; the stomach requires excitement to rally its energies, and the temperate use of wine and condiments becomes essential to health; or, as often happens to men of studious habits, who when taking little exercise suppose that they have only to live abstemiously to guard their health, the stomach breaks down, and several years of dyspepsia are the destructive consequence of imprudent literary excesses.

CHAPTER VIII.

OF THE LACTEAL AND LYMPHATIC VESSELS.

We have next to follow the route of the chyle from the small intestines into the venous system. In the year 1622 Aselli observed upon the mesentery of a dog white lines extending from the bowel towards the liver: on puncturing them a milk-like fluid escaped, and left them transparent vessels. They were termed lacteals, and were justly supposed by their discoverer to absorb the chyle and convey it into the blood. Successive inquiries have shown not merely the origin and termination of these vessels, but that they form part of a system as minutely distributed through the frame as the blood-vessels, and theoretically termed the absorbent system.

At the angle formed by the meeting of the subclavian with the internal jugular vein upon either side of the neck, two or more of these pellucid vessels open, so as to pour their contents into the current of blood passing towards the right auricle. These are the trunks of the absorbent system, which branches from the subclavian veins to every region and organ of the body, but communicates at no other point with the blood-vessels.

The thoracic duct, the largest absorbent in the body, is about three lines in diameter when distended, is of a thin but strong texture, and appears when collapsed semitransparent and of a reddish grey colour.

N

The

178 Structure of Lacteal and Lymphatic Vessels.

thoracic duct of a horse, inverted upon the thickest rod it will admit, is shown by the rupture of its lining membrane to consist of a serous inner tunic and an outer fibrous one. It is presumed that a similar distinction of parts exists in human absorbents".

Each absorbent vessel contains many valves, consisting of pairs of semilunar folds of membrane attached by their convex edges, as in the veins, and capable of being thrown down by the reflux of its contents so as to close the passage from the trunks towards the branches. Upon the fleshy viscera the resistance of the valves may be overcome by continued pressure, so that mercury will pass from a trunk into the branches, which are there found to be distributed arborescently, with a minuteness so surprising, that the surface of the viscus is entirely covered as with a reticular sheet of quicksilver. These vessels appear to anastomose with a series distributed through the substance of the organ.

In the limbs the absorbent trunks are distributed in two sets; one that accompanies the arteries, another which accompanies the subcutaneous veins: to each artery from three to seven trunks are attached; with the subcutaneous veins from thirty to fifty are associated, which spread over the most protected regions of the limbs.

At particular parts of the body small flattened bodies circular or oval, from three to ten lines in diameter, are found connected with absorbent vessels. These bodies are termed conglobate or absorbent glands. They are very vascular, and have filaments of nerves distributed

[ocr errors]

Cruikshank. Anatomy of the Absorbing Vessels, p. 61.

« AnteriorContinuar »