PHYSIOLOGY OF DIGESTION.

127

two other secretions, the pancreatic juice and the bile from the liver. In the stomach and along the intestine, there is an absorption going on by two different ways. The one is by the lacteal vessels: these have the exclusive power of taking up the fatty matters, which constitute the chief part of the chyle, as their contents are named. The other is by the capillary blood vessels, by whose means the nutritive matter is taken at once into the circulation, but before reaching the heart it passes through the liver. The use of the pancreatic juice, which is poured into the intestine near its commencement, is to co-operate with the salivary glands in dealing with the starchy constituents of the food, and to cor tribute, probably along with other fluids, to the digestion of the fat. The functions of the liver are more complex and obscure. The bile appears to aid in the digestion of the alimentary matters; mixing with the fatty matters of the food, it is indispensable to their being absorbed in the intestines. The liver is further believed to form sugar and fat out of other elements passing into it by the circulation. The blood from the intestines, before returning to the heart, passes through the liver, and takes up the sugar formed independently there. In coursing through the intestine by the successive contractions of the tube, the material is lessened by absorption into the lacteals and blood vessels; at the same time it gathers new matter by secretion from the coats of the intestines, which matter is of the impure kind, and is destined to pass out of the system along with the husk and undigested remainder of the food.

Only the upper and lower ends of the alimentary canal are supplied with cerebro-spinal nerves. The vagus nerve is largely distributed to the stomach, and nerves from the same system to the rectum, but the intestine receives its supply from the sympathetic system. This corresponds with our experience of alimentary sensations, which are concentrated chiefly in the two extremities of the canal, while the intervening thirty feet of intestine is almost entirely without sensation in ordinary circumstances. The movements of the

intestine are kept up by means of the sympathetic system of

nerves.

19. And now with regard to the Feelings of Alimentary action. These are of the pleasurable kind when the action is healthy; pains are the result of disease and disorder.

Discussing first the sensation of taking food, we shall find a pretty general agreement as to its character. I do not speak of the feeling of Taste, but of the sensibility connected more particularly with the stomach, which extends even to the mouth in connexion with salivation, and is called relish. If we include the entire mass of sensation arising from a healthy meal, and lasting a certain time after the meal is finished, at which stage the operation of digestion in the stomach is the sole cause of what we feel, we may safely pronounce it to be an agreeable state of a high order. It has the characteristic of massiveness, or quantity, being a rich, luxuriant, satisfying sensation. Such is the character common to all kinds of healthy nourishment; but there is the greatest possible difference in the qualities of food as regards stomachic relish; from turtle to stale oat-cakes, or a piece of black bread, what a mighty interval! To the richer kinds of food belong a feeling intense as well as voluminous. The magnitude of the sensation is attested by its ability to submerge a great many irritations, and to make itself for the time the ruling element of the consciousness. This power brings it into comparison with such feelings as healthy exercise and repose, nervous elation, and the intoxication of warmth.

The energy of the Volition corresponds to the relish and to the stage of the operation. At first, the stimulus to action is intense and even furious. Appetite is infamed by partial gratification; and until such time as the stage of fullness draws near, the pleasure shows itself in supplying impulse to continue it. Eating is among the most characteristic examples of the general law of Feeling-prompted Action that we can produce, being not only for the avoidance of pain, but also for the retaining and heightening of pleasure.

To complete the delineation of this mode of consciousness,

we may notice the peculiarity of it as related to the Intellect. Here, however, we have only to repeat what has been said on most of the feelings hitherto discussed, that there is comparatively little permanence in idea when the state of the organs is such as to forbid the reality. But the reality is one that can never be long absent. As a general rule, it is true of digestive and all other organic sensations, that they are exceedingly powerful when present, and exceedingly little realized when absent. They are very unlike sights and sounds, loves and hatreds, and other states that the intellect can retain in the ideal form; to imagine with effect the relish of a feast when under nausea, passes the power of the most vigorous memory.

The sensation connected with the lower extremity of the canal is chiefly of the nature of a feeling of relief from pain.

20. Another important healthy sensation of the alimentary canal is Hunger, the state preparatory to the one just described.

The physical concomitants of hunger are a collapsed condition of the stomach, and a deficiency of nutritive material in the system. The sensitive nerves distributed to the mucous surface of the stomach are first affected, then the nerves of the lower intestines, and finally an influence of the general system adds to the pain and the feeling of depression. It is considered probable that the state of the muscular fibres of the stomach makes a part of the case.-(WEBER.) These are at first loose and uncontracted, but at a later stage their characteristic (peristaltic) movements are commenced upon the empty tube. The cutting of the nervus vagus (supplying the mucous surface) does not entirely abolish the feeling of hunger. The feeling itself is of the uneasy or painful class, with a degree of massiveness and engrossment corresponding to stomachic feelings in general.

The appetite for eating commences with a pleasant feeling, and consists of certain indefinite sensations in the region of the stomach, accompanied by stimulation of the muscles of chewing, and by the secretion of saliva. This passes next

into an uneasy feeling; then come on oppressive gnawing pains, which are referred to the region of the stomach; these are followed by sensations of a still stronger kind derived from a more general action, under which the local feelings are submerged. This last is the state of inanition, or starvation.

Animals are driven in search of food after the nervus vagus is cut; which would seem to imply that the sense of starvation in the body generally is a part of the motive power of hunger. On the other hand it is contended, that when the digestion is diseased, the appetite for food is entirely wanting, however much the frame be suffering from want. The influence of the nerves and the nerve centres is shown in the fact, that a desire of eating may exist when the stomach is full. In ordinary circumstances, the state of fullness of the stomach is followed by the sensation of Satiety.

21. The feeling of Nausea and Disgust is an effect indicating some great disturbance in the usual course of digestive operations. This state is associated with the act of vomiting, an act that may take place, '1. from the introduction of certain substances into the stomach, some of which, as bile, mustard, common salt, not becoming absorbed, must act simply by the impression they make on the mucous membrane; 2. By the introduction of emetics, as Tartar emetic, into the blood, or by the presence of certain morbid poisons in the fluid; 3. By mental emotion, as that excited by the sight of a disgusting object; 4. By irritation at the base of the brain.'-TODD and BOWMAN, II., p. 214. To these must be added sea-sickness. Inflammation of the brain in children usually shows itself first in violent vomiting. The act of vomiting is the result of a reflex stimulus, directed towards the muscles that compress the abdomen in the act of expiration of the breath. These muscles violently contracting, while the exit of the air from the lungs is shut up, squeeze the contents of the stomach upwards towards the mouth. The sensation of vomiting is in most cases horrible in the extreme. It proves by a strong instance the power of stomachic influences on the nervous

system. The sensation is one sui generis-no other feeling can at all compare with it. There are many forms of unendurable pain, but this has a virulence of its own, great both in quantity and in intensity. On the maxim that the abuses of the best things are the worst, the wretchedness of stomachic perversion would be a testimony of the aptitude for pleasure belonging to this part of the system.

The sensations of nausea are also accompanied by irregular movements of the muscles of the pharynx. These are the seat of the characteristic feeling of nausea. In the stomach also, the sensation may be connected with irregular, or antiperistaltic movements in the muscular fibres.

The feelings of nausea and disgust, and the objects causing them, are expressed in our language by a variety of strong terms. The 'disagreeable' is originally what revolts the stomach, extended in its application to other forms of the unpleasing. Disgust' is the extreme opposite of relish. The fact that these words are among the strongest that the language affords to express dislike or aversion, proves how deep and intense is the feeling that they primarily refer to.

Besides the objects that produce disgust by actual contact with the alimentary canal, there are substances whose appearance to the eye is disgusting. Certain gases also affect the smell in the same way. Disgusting sights are mostly the result of association; but some nauseous smells act from the very beginning. The arrangements of human life, particularly address themselves to our protection against disgusts; and singularly enough, the chief things to be avoided are the products of living bodies themselves. This is the foremost aim of the operations of cleansing and the removal of refuse. The influences that stimulate a healthy digestion and relish are contrasted with their opposites by the term fresh,' which we spoke of already as a quality of respiration, but which has still more emphasis as opposed to the causes of disgust. The power of resisting nauseating influences is an indication of great stomachic vigour in the right direction.