Essentials of Physiology (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...part, the latter being perhaps transformed into glycogen, dextrose, or fat before it is utilized by the cells. It is known that these substances may be formed from proteid food, as has been stated above. It seems probable that fats and carbohydrates never form part of the bioplasm, but are held closely in contact with it within the cells, and utilized by it as a source of energy. Some of the proteid food is undoubtedly transformed into the living proteid of bioplasm, but it is unlikely that it all undergoes this process before being oxidized. In all likelihood, the fats, the carbohydrates, and most of the proteid, alter entering the cell, suffer decomposition without ever becoming a part of bioplasm. Some of their decomposition products may subsequently undergo synthesis; for example, sugar may in this way be transformed into fat. The proteid of bioplasm, or, as it is called, tissue proteid, may be supposed to break down but slowly; at the rate, it has been estimated, of about 1 rfo per diem. By far the greater part of the proteid metabolism occurs in the muscles, and the most characteristic feature of muscle is its power of contraction, yet no relation exists between muscular activity and proteid metabolism. Muscular work is accomplished at the expense of the nonnitrogenous food-stuffs, namely, carbohydrates and fats; for the excretion of nitrogen is hardly affected by exercise, unless it be very violent, or unless there be a scarcity of fats and carbohydrates in the diet. On the other hand, muscular exercise is accompanied by a great increase in the excretion of carbon dioxid. Not all the energy liberated during contraction appears in the form of mechanical work; the larger portion is given off as heat. In the absence of a sufficient supply of nonproteid ...