Briefly stated, all food-stuffs when minutely studied chemically, are found to be composed of three distinct classes of compounds.

First, the inorganic substances, or those which enter the system under their own form, pass through unchanged, and come out in the same shape that they entered. They assist the economy physically rather than by chemical activity.

Second, the carbohydrate and hydrocarbon compounds, such as the starches, sugars, and fats. All of this group act primarily through chemical action, being oxidized into carbon dioxide and water with the production of heat.

Third, the proteids, of which there are two grand classes; the vegetable proteids, or those existing in a polymeric state, and the animal proteids, which are in the form of single molecules. Out of this class alone can all the proteid structures of the body be formed, either by a process of isomeric transmutation or by physical anabolism.

It matters little how complex the meal, the starches. and sugars of all kinds have to be transmuted in part by the ferment ptyalin, but chiefly by the amylopsin, in the intestinal canal into a definite molecular form called glu

cose.

This accomplished, certain epithelial cells lining the small intestines have for their special function the absorption of this particular molecular form, which we call glucose, into their protoplasmic structure. In the substance of the cell, the molecule is isomerically transformed, so that when it is discharged, as it is eventually, into the entero hepatic circulation, it no longer responds to the common tests for glucose. From the entero-hepatic blood this

carbohydrate compound passes into the substance of the hepatic cells, together with active oxygen brought to the liver by the oxyhemoglobin. Within the hepatic cells the oxygen attacks this compound and oxydizes it into carbon dioxide and water-as illustrated in the diagram-with the production of heat equivalent to 1657 kilogram-meters of work for each gramme of the carbohydrate thus consumed. Thus this oxidation process with its heat production becomes one of the prime factors in maintaining nerve action, and, by being applied to the peripheral nerve endings, is, through the centripetal nerves, brought into direct relation with the central nervous system. It is by this constant heat production in the glandular organs of the body that nerve action is set in motion and maintained in action. Through this reflected nerve impulse from the periphery to the cerebral nervous system, and from the centre back to all parts of the animal economy, a harmonious balance of activity is developed and sustained throughout the whole system. All nerve action, therefore, takes its origin in the oxidation processes which are constantly occurring in the epithelial cells which constitute the coating of the body. These surface cells when bunched together, as they are in the liver and the salivary, pancreatic, and renal glands, etc., are found to be the chief oxidizing zones of the body.

The animal and vegetable fats, like the starches and sugars, are transmuted chiefly in the alimentary canal by the action of the ferment bodies found in the pancreatic, biliary, and intestinal secretions.

The animal fat is transmuted in part into a fine emulsion, and in part into its components, a fatty acid and glycerin, the former joining with a soda compound to

form a soap. The emulsified fat is drawn into the protoplasm of those epithelial cells which have for their particular function the taking up of fat. From the substance of these cells the fat-globules are discharged into the underlying lymphatics in the villi that support the epithelial cells. From this terminal lymphatic, which is a slight bulbous expansion ensheathed with muscle fibers, the fat is driven on to the deeper lymphatics, on through the thoracic duct, and finally enters the blood-stream at the point of origin of the left brachio-cephalic vein. Having gained access to the blood-stream at this point, the fat passes on with the blood to the right heart, and through this organ to the lungs. From the pulmonary capillaries the fat appears to be taken up, together with active oxygen, into the epithelial cells that line the air-sacs, and by a process of oxidation, the fat is here converted into carbon dioxide and water, with the production of heat. Thus, for each gramme of fat consumed in this manner in the lungs, the heat equivalent of 3841 kilogram-meters is produced. This heat stimulates the peripheral nerve-endings in the lungs with the same concomitant phenomena as were described in connection with the heat production in the liver by the oxidation of carbohydrate compound.

The soap and glycerin produced by the action of the ferment steapsin are a part of the laxative mixture which the system must produce each day to keep the bowels in motion and prevent constipation. The vegetable fats being less perfectly emulsified and more easily decomposed, are more likely to be cathartic in action and poor heat producers.

The proteids, or true tissue builders, all enter the alimentary canal in the form of alkali-albumin, either

in the polymeric state, as found in the vegetable kingdom, or the "monomeric " form common to animal fluids and solids. In the alimentary canal the polymeric form must first be transmuted into the simpler form. This accomplished, alkali-albumin is acted upon by the hydrochloric acid, and isomerically transmuted into acid-albumin, after which it is further acted upon by the ferment body pepsin and transmuted into a series of albumoses, and finally into a true peptone, which is the only form in which a proteid. can be taken up by the epithelial cells of the alimentary canal. The larger percentage of the proteids in the foodstuffs, however, passes through the cavity of the stomach into the intestinal canal unpeptonized. Thus we find that the function of the stomach is chiefly a storage and macerating tank, the major portion of the proteids, as well as the starches, sugars, and fats being transmuted in the intestinal canal. The ferment body trypsin, secreted by the pancreatic gland, together with the protolytic ferments of the bile and intestinal secretions, complete the peptonization of the proteids. When they have all been converted into this particular form in which the proteid can be drawn into the protoplasmic substance of the epithelial cells, they are absorbed by these special cells. After the peptone has gained access to the protoplasm of these cells, of which there are three distinct sets as regards their functions, it is further isomerically transmuted. One set of cells discharges the contained proteid into the entero-hepatic blood-stream as serum-albumin, another as serum-globulin, and a third as fibrinogin.

If the transmuting function of these cells is over-taxed, the peptone may be discharged as such into the enterohepatic blood. The peptone being a toxic form of proteid,

when it reaches the hepatic gland, the epithelial cells of the liver take up the peptone and transmute it into a non-toxic form, in a manner similar to that of the cells of the intestinal canal when they are performing their function normally, thus preventing general toxemia from the peptones.

After the proteid body has reached the enterohepatic blood-stream in the normal manner and has been properly transformed, it passes on, in one of those three forms, from structure to structure, being changed from one form to another, thus giving a different physical character and function to the various organs and structures of the body without undergoing any decided chemical decomposition, a small portion being thus transmuted to form the ferment bodies secreted by the glandular organs of the alimentary canal.

When the proteid has served its purpose to the body, it is again taken up into the protoplasm of the epithelial cells covering the body, chiefly into the cells which constitute the excretory organs, such as the liver and kidneys. At the same time that the proteid enters the cell, oxygen is introduced from the oxyhemoglobin of the blood into the protoplasm. This results in an active chemical decomposition or oxidation of the proteid, with the formation of the katabolic products, which are common to the excreta. Each gaamme of proteid oxidized in the body yields the heat equivalent of 1812 kilogram-meters.

With this understanding of the composition and utilization of the food-stuffs, if the food-supply is properly adjusted so that the constructive material is available and sufficient for the daily demands of the system, and if, at the same time, the heat-producing substances are of the