CRYSTALLOID IN LIVING CEM > 29 



In other types of cell these differences in osmotic pressure 

 within and without the cell become enormously greater. Thus, 

 in plants, the root sap which carries up the electrolytes from the 

 earth for the nutrition of the growing .cells is exceedingly dilute, 

 the depression of freezing point being only about one-fifth part 

 of that of the cell juice. Similarly, in the secretion of sweat and 

 saliva the concentration of inorganic ions, as shown both by freezing 

 point methods and by direct chemical analyses, is only a small 

 fraction of that of the plasma or lymph. In other cases, such 

 as absorption by the intestinal cells and secretion by the kidney 

 cells, the osmotic pressure on the side remote from the lymph may 

 lie either above or below that on the lymph side, but nearly always 

 differs widely from it. It has been shown that either distilled 

 water or hypertonic salines can be taken up by the intact intestinal 

 mucosa ; and the A (i.e. freezing-point depression) of the urine 

 may be many times greater than that of the plasma, or may 

 after ingestion or intra-venous injection of much water be a mere 

 fraction of the A of the plasma. 



Whether the tremendous pressure differences corresponding to 

 these differences in A really exist within the cells must remain 

 indeterminate so long as we possess no knowledge as to the degree 

 to which the crystalloids of the secretion are adsorbed while the 

 secretion is passing through the cell and is in contact with the 

 bioplasm. By alternating or periodic dissociation and combina- 

 tion between colloid and crystalloid in the actively secreting (ab- 

 sorbing or excreting) cell, the pressures would appear and disappear 

 alternately ; and if by the action ot the nerve supply or any stimu- 

 lating substance the bioplasm is thrown into any such rhythmic 

 activity of adsorption and re-separation, there would follow an 

 easy explanation of the passage of both water and crystalloid 

 through cells, in any concentration. For the concentration would 

 depend solely on the uptake of crystalloid by the cell colloid, before 

 the next explosion, disrupting colloid and crystalloid, threw the 

 crystalloid free in the cell and determined, by the osmotic pressure 

 developed thereby in the cell, the flow of secretion. 



It would appear that in nerve and muscle at the period of 

 activity only, and in injured tissue (which is excited or active 

 tissue), there exists in reality a detachment of potassium ions from 

 the colloid which does not exist before or after the active period 

 (Macdonald). 



