Respiration

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...or part of an organism is distinctly specific. The percentage and nature of each of the substances which we can recover on disintegrating the living tissue are specific; and the more we learn about the nature of these substances the more clearly does this specific character emerge. It is evidently no mere accident that muscle yields so much potassium, so much phosphoric acid, so much water, and so much of various proteins. These substances must be present in some kind of combination in the living "substance"; and if so the living substance cannot be regarded as a mere solution of free molecules. The molecules are in some sense bound, as they are in a solid; and in so far as this is the case the living substance must in certain respects behave as a solid, impervious to the free passage of material by diffusion. The layer of thin flattened epethelium lining appears to be gastight (to oxygen at least) except where it covers the oval. At this point the layer allows gas to pass freely. From this point of view we can understand why the living cells of the oxygen-secreting gland should be gas-tight, or nearly so, against diffusion backwards, but we have not yet considered how the gas passes forward through them during secretion; and if "living material" behaved like an ordinary solid no such explanation would be forthcoming. But evidently a living cell does not behave like an ordinary solid: for it is constantly taking up and giving off material, not merely during secretion, but at every moment of its existence. This is evident from a general consideration of the phenomena of nutrition, and becomes still more evident if by altering the environment of a cell we disturb the labile balance between living cells and their...