Part 18 (1/2)

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.