intensity, as in a hot bath, a warm room, a warm bed. The hot bath is the extreme instance. By no other contrivance can such a mass of heat be brought to bear upon the human system; consequently this presents the sensation of warmth in its most luxuriant form; a sensation cherished with intense avidity while it lasts, and surrendered with great reluctance. It is the intoxication of animal heat. We are unavoidably led to assume that this warmth must act in a very direct way upon the nerves; for it is not to be supposed that the organic processes are so very much furthered by the sustained temperature as to exalt the pleasurable consciousness to so remarkable a degree. I prefer rather to assume that both the cold shiver and the warm glow are due in a great measure to a direct influence of temperature on the substance of the nerves; although, as above remarked, there can be no doubt of the deranging influence of cold upon organic life. Nevertheless, we may derange the system by excessive heat, without producing the painful feeling arising from cold; the instances of scorching fires, hot liquors, and a burning sun will satisfy most people on this head.

As cold increases the action of the lungs and the circulation, so warmth enfeebles both; and hence, with all its pleasurableness, makes the body less disposed to action, as is seen in summer heat and in tropical climates. This effect, however, is not without a good side; for in the case of morbid activity of the nervous system, warmth is a soothing influence, either by its physical effects, or by the nature of the sensation, which, like repose, is eminently satisfying and anti-volitional, or from the physical and mental effects combined.

Sensations of the Alimentary Canal.

There is

12. Digestion offers all the conditions of a sense. an external object,-the Food; a distinct organ of sense,-the Alimentary Canal and its appendages; and a set of Feelings arising from the contact, also distinct and specific. To treat these feelings under Taste is to confound together two senses totally different in their character, although happening to have one common object or stimulant.

OBJECTS OF THE ALIMENTARY SENSE.

135

13. The objects of this sense are the materials taken into the body as food and drink. These materials are extremely various, but there is no corresponding variety in their action on the stomach. They can be reduced to a few general heads, according to their composition, it being found possible to assign a few leading substances which comprehend all the different sorts of material serviceable in nourishing the body. The following is an abstract of this classification:

Ist. Water and the watery liquids, including the substances conveyed in solution, or suspension, in water.

2nd. Saccharine substances, derived from the vegetable kingdom. This comprehends sugars, starch, gums, vinegar.

3rd. Oily substances. These include the various fats and oils, as well as alcohol. Like the former group, they are composed of carbon and the elements of water, but in them the carbon is in a much higher proportion.

4th. Albuminous substances, containing nitrogen fibrine, gelatine, albumen, caseine (matter of cheese), vegetable gluten, 'all the materials which make up this group are derived generally from the animal kingdom, with the exception of the last, which is contained in great abundance in wheat; similar if not identical, principles exist in other vegetables. Wheat, indeed, consists of two substances-one referable to the saccharine group, the other to the albuminous, the former consisting of starch, the latter of gluten.'

Milk is found to contain matter of all the four classes: water, sugar, oily matters (butter), caseine.

The three first classes are incapable of nourishing the principal animal tissues, such as nerve, muscle, &c. They are fitted rather for supplying fat, bile, and matters used in the production of the carbonic acid that escapes from the lungs. They are chiefly destined for the creation of animal heat, which in the main seems to arise from the conversion of carbon into carbonic acid. The fourth class, or the albuminous substances, are the proper elements of nourishment, having a composition fitting them for that purpose.-TODD and BOWMAN, II. 152, 3.

The differences that exist among the infinity of articles

used as food are not at bottom so great as they seem. If we take the different species of grain,-wheat, barley, rye, oats, rice, maize, millet, we shall find they are all composed of the same ultimate materials, gluten and starch, though not in the same proportions. In like manner the potato is a starchy vegetable, with a very small share of gluten, hence the defective character of it as an article of nourishment. Another difference among vegetables relates to their texture, as fitting them for being acted on during mastication and digestion,-a circumstance, however, which cooking can modify. Thus the potato is a much looser texture than grain. A third point of distinction among alimentary substances is the extraneous essences that may enter into them and affect the sense of taste and the general relish, as in the difference between mutton and beef, chicken and venison, brandy and rum. Such elements belong more to Taste than to Digestion, although this last function may be influenced by extraneous additions, as mustard and spices.

14. I extract from Quain's Anatomy the following general view of the Organs of Digestion.

"The digestive apparatus includes that portion of the organs of assimilation, within which the food is received and partially converted into chyle, and from which, after the chyle has been absorbed, the residue, or excrement, is expelled. It consists of a main or primary part named the alimentary canal, and of certain accessory organs.

'The alimentary canal is a long membranous tube, commencing at the mouth and terminating at the anus, composed of certain tunics or coats, and lined by a continuous mucous membrane from one end to the other. Its average length is about thirty feet, being about five or six times the length of the body. The upper part of it is placed beneath the base of the skull, the succeeding portion is situated within the thorax, and the remainder is contained within the cavity of the abdomen. In these several situations, its form, dimensions, and connexions, its structure and functions, are so modified, that certain natural divisions of it, bearing different names, have been recognised by anatomists.

ORGANS AND PROCESSES OF DIGESTION.

137

'It may he considered as composed of two parts; one situated above the diaphragm, and the other below that muscular partition, and therefore within the abdomen. The first division consists of the organs of mastication, insalivation, and deglutition; and comprises the mouth, the pharynx, and the œsophagus, or gullet. The second division consists of the organs of digestion, properly so called, and of those of defæcation; viz., the stomach, the small intestine, and the great intestine.

'The accessory parts are chiefly glandular organs, which pour their secretions into it at different points. They consist of the salivary glands (named the parotid, submaxillary, and sublingual), the liver, and the pancreas. Besides these large glandular organs, a multitude of small glands, compound, follicular, or tubular, are collected together at certain points, or scattered over large portions of the inner surface of the alimentary canal: these are described along with the mucous membrane of each part. The remaining accessory organs are the teeth, the jaws, the tongue, and the spleen.'-p. 965.

15. The physiology of digestion must be very briefly stated here. The first stage is mastication, which serves the double purpose of breaking down the food and mixing it with saliva; the function of the saliva is now known to be to convert the starch into grape sugar by a process of the nature of fermentation. The effort of mastication is purely voluntary, but when the food gets upon the back part of the tongue it is passed into the bag of the pharynx, and propelled down the gullet into the stomach by involuntary muscular contractions. In the stomach it is exposed to the action of the gastric juice. This peculiar action is not as yet fully understood, but so far as the researches of physiologists have yet gone, the most reasonable conclusion is, that in man and the carnivora the fluid secreted by the stomach during digestion simply dissolves animal and vegetable substances of the azotized kind, so as to render them capable of absorption, without materially altering their chemical constitution, leaving starchy, oily, saccharine, and the allied substances but little or not at all acted on.' The matter that leaves the stomach to pass into the intestines, is known by the

name of chyme. This is very soon mixed up with 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 constitutes 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 cooperate with the salivary glands in dealing with the starchy constituents of the food, and to contribute 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; its abundant hydro-carbonous ingredients are in great part absorbed in its passage along the intestine, while other constituents are finally discharged as excrementitial. The liver is further believed to form sugar and fat out of other elements passing into it by the circulation. 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. The extremity of the great intestine is called the rectum, and on it are brought to bear the muscles of final expulsion.

It is important to be remarked before passing to the consideration of the states of consciousness allied with digestion, that 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 inter