267. In the process of digestion, the food is subjected to five different changes. 1st. The chewing and admixture of the saliva with the food; this process is called _mastication_.

268. 2d. The change through which the food pa.s.ses in the stomach by its muscular contraction, and the secretion from the gastric glands; this is called _chymification_.

269. 3d. The conversion of the h.o.m.ogeneous chyme, by the agency of the bile and pancreatic secretions, into a fluid of milk-like appearance; this is _chylification_.

270. 4th. The absorption of the chyle by the lacteals, and its transfer through them and the thoracic duct, into the subclavian vein at the lower part of the neck.[9]

[9] The chyle is changed by the lacteals and mesenteric glands, but the nature of this change is not, as yet, well defined or understood.

271. 5th. The separation and excretion of the residuum.

272. Perfection of the second process of digestion requires thorough and slow mastication. The formation of proper chyle demands appropriate mastication and chymification; while a healthy action of the lacteals requires that all the anterior stages of the digestive process be as perfect as possible. (Appendix F.)

267. Recapitulate the five changes in the digestive process.

_Note._ Let the pupil review the anatomy and physiology of the digestive organs from figs. 62 and 65, or from anatomical outline plate No. 5.

[Ill.u.s.tration: Fig. 65. An ideal view of the organs of digestion, opened nearly the whole length. 1, The upper jaw. 2, The lower jaw. 3, The tongue. 4, The roof of the mouth. 5, The oesophagus. 6, The trachea. 7, The parotid gland. 8, The sublingual gland. 9, The stomach. 10, 10, The liver. 11, The gall-cyst. 12, The duct that conveys the bile to the duodenum, (13, 13.) 14, The pancreas. 15, 15, 15, 15, The small intestine. 16, The opening of the small intestine into the large intestine. 17, 18, 19, 20, The large intestine. 21, The spleen. 22, The upper part of the spinal column.]

CHAPTER XV.

HYGIENE OF THE DIGESTIVE ORGANS.

273. It is a law of the system, that each organ is excited to healthy and efficient action, when influenced by its appropriate stimulus.

Accordingly, nutrient food, that is adapted to the wants of the system, imparts a healthy stimulation to the salivary glands during the process of mastication. The food that is well masticated, and has blended with it a proper amount of saliva, will induce a healthy action in the stomach. Well-prepared chyme is the natural stimulus of the duodenum, liver, and pancreas; pure chyle is the appropriate excitant of the lacteal vessels.

274. The perfection of the digestive process, as well as the health of the general system, requires the observance of certain conditions.

These will be considered under four heads:--1st. The _Quant.i.ty_ of food that should be taken. 2d. Its _Quality_. 3d. The _Manner_ in which it should be taken. 4th. The _Condition_ of the system when food is taken.

275. The QUANt.i.tY of food necessary for the system varies. Age, occupation, temperament, temperature, habits, amount of clothing, health and disease are among the circ.u.mstances which produce the variation.

273-330. _Give the hygiene of the digestive organs._ 273. Give a law of the system. What is the appropriate stimulus of the salivary glands during mastication? Of the stomach? Of the duodenum? Of the lacteal vessels? 274. What does the perfection of the digestive organs require? 275. What exert an influence on the quant.i.ty of food necessary for the system?

276. _The child and youth require food to promote the growth of the different parts of the body._ The more rapid the growth of the child, the greater the demand for food. This accounts for the keen appet.i.te and vigorous digestion in childhood. When the youth has attained his full growth, this necessity for nutriment ceases; after this period of life, if the same amount of food is taken, and there is no increase of labor or exertion, the digestive apparatus will become diseased, and the vigor of the whole system diminished.

_Observation._ When the body has become emaciated from want of nutriment, either from famine or disease, there is an increased demand for food. This may be gratified with impunity until the individual has regained the usual size, but repletion should be avoided.

277. _Food is required to repair the waste, or loss of substance that attends action._ In every department of nature, waste, or loss of substance, attends and follows action. When an individual increases his exercise,--changes from light to severe labor,--or the inactive and sedentary undertake journeys for pleasure, the fluids of the system circulate with increased energy. The old and exhausted particles of matter are more rapidly removed through the action of the vessels of the skin, lungs, kidneys, and other organs, and their places are filled with new atoms, deposited by the small blood-vessels.

278. As the chyle supplies the blood with the newly vitalized particles of matter, there is, consequently, an increased demand for food. This want of the system induces, in general, a sensation of hunger or appet.i.te, which may be regarded as an indication of the general state of the body. The sympathy that exists throughout the system accords to the stomach the power of making known this state to the nervous system, and, if the functions of this faithful monitor have not been impaired by disease, abuse, or habit, the call is imperious, and should be regarded.

276. At what age is the appet.i.te keen and the digestion vigorous? Why?

What is said in regard to the quant.i.ty of food when the youth has attained his growth? What exception, as given in the observation? 277.

Give another demand for food. What effect has increased exercise upon the system? 278. How are the new particles of matter supplied? What does this induce?

279. _When exercise or labor is lessened, the quant.i.ty of food should be diminished._ When a person who has been accustomed to active exercise, or even hard manual labor, suddenly changes to an employment that demands less activity, the waste attendant on action will be diminished in a corresponding degree; hence the quant.i.ty of food should be lessened in nearly the same proportion as the amount of exercise is diminished. If this principle be disregarded, the tone of the digestive organs will be impaired, and the health of the system enfeebled.

280. This remark is applicable to those students who have left laborious employments to attend school. Although the health is firm, and the appet.i.te keen from habit, yet every pupil should practise some self-denial, and not eat as much as the appet.i.te craves, the first week of the session. After some days, the real wants of the system will generally be manifested by a corresponding sensation of hunger.

_Observation._ It is a common observation that in academies and colleges, the older students from the country, who have been accustomed to hard manual labor, suffer more frequently from defective digestion and impaired health than the younger and feebler students from the larger towns and cities.

281. _Food is essential in maintaining a proper temperature of the system._ The heat of the system, at least in part, is produced in the minute vessels of the several organs, by the union of oxygen with carbon and hydrogen, which the food and drink contain. The amount of heat generated, is greatest when it is most rapidly removed from the system, which occurs in cold weather. This is the cause of the system requiring more food in winter than summer.

279. Why should the quant.i.ty of food be diminished when the exercise is lessened? What effect if this principle be disregarded? 280. To what cla.s.s is this remark applicable? What is often observed among students in academies and colleges? 281. State another demand for food. What is one source of heat in the body?

_Observation._ Persons that do not have food sufficient for the natural wants of the system, require more clothing than those who are well fed.

282. The last-mentioned principle plainly indicates the propriety and necessity of lessening the quant.i.ty of food as the warm season approaches. Were this practised, the tone of the stomach and the vigor of the system would continue unimpaired, the "season complaints" would be avoided, and the "strengthening bitters" would not be sought to create an appet.i.te.

_Observation._ Stable-keepers and herdsmen are aware of the fact, that as the warm season commences, then animals require less food. Instinct teaches these animals more truly, in this particular, than man allows reason to guide him.

283. _The quant.i.ty of food should have reference to the present condition of the digestive organs._ If they are weakened or diseased, so that but a small quant.i.ty of food can be properly digested or changed, that amount only should be taken. Food does not invigorate the system, except it is changed, as has been described in previous paragraphs.

_Observation._ When taking care of a sick child, the anxiety of the mother and the sufferings of the child may induce her to give food when it would be highly injurious. The attending physician is the only proper person to direct what quant.i.ty should be given.

Why do we eat more in the winter than in the summer? What practical observation is given? 282. Why should the quant.i.ty of food be lessened as warm weather commences? What would be avoided if this principle were obeyed? 283. Why should the present condition of the digestive organs be regarded in reference to the quant.i.ty of food? Mention an instance in which it would be injudicious to give food.

284. _The quant.i.ty of food is modified, in some degree, by habit._ A healthy person, whose exercise is in pure air, may be accustomed to take more food than is necessary. The useless excess is removed from the system by the waste outlets, as the skin, lungs, liver, kidneys, &c. In such cases, if food is not taken in the usual quant.i.ty, there will be a feeling of emptiness, if not of hunger, from the want of the usual distention of the stomach. This condition of the digestive organs may be the result of disease, but it is more frequently produced by inordinate daily indulgence in eating, amounting almost to gluttony.

285. _Large quant.i.ties of food oppress the stomach, and cause general languor of the whole body._ This is produced by the extra demands made on the system for an increased supply of blood and nervous fluid to enable the stomach to free itself of its burden. Thus, when we intend to make any extraordinary effort, mental or physical, at least for one meal, we should eat less food than usual, rather than a greater quant.i.ty.

286. _No more food should be eaten than is barely sufficient to satisfy the appet.i.te._ Nor should appet.i.te be confounded with taste.

The one is a natural desire for food to supply the wants of the system; the other is an artificial desire merely to gratify the palate.

287. Although many things may aid us in determining the quant.i.ty of food proper for an individual, yet there is no certain guide in all cases. It is maintained by some, that the sensation of hunger or appet.i.te is always an indication of the want of food, while the absence of this peculiar sensation is regarded as conclusive evidence that aliment is not demanded. This a.s.sertion is not correct, as an appet.i.te may be created for food by condiments and gormandizing, which is as artificial and as morbid as that which craves tobacco or ardent spirits. On the other hand, a structural or functional disease of the brain may prevent that organ from taking cognizance of the sensations of the stomach, when the system actually requires nourishment.