INTRINSIC ACTIVITY OF SECRETING CELLS 151 



On the other hand, with increasing osmotic pressure of oxygen 

 in the plasma above the point at which oxy- hemoglobin has been 

 completely formed, there is but little further uptake of oxygen 

 by the red blood- corpuscle ; and similarly in the case of the 

 potassium ion, or any other active ion, in the plasma above the 

 concentration at which the protoplasm of the tissue cell has been 

 saturated, the uptake of potassium ion by the cell will be small 

 and inappreciable to chemical investigation, so that even in an 

 isotonic or somewhat hypertonic solution of potassium salt alone 

 the amount of potassium ion taken up by the cell will not be 

 appreciably greater to ordinary chemical analysis than that taken 

 up from normal plasma where the osmotic pressure of potassium 

 ion is many times lower, but still sufficiently high to cause almost 

 complete association between the protoplasm and the potassium 

 ion. Although the difference in uptake of either oxygen or 

 potassium ion is so small as to escape chemical determination, 

 it may, however, produce in both cases profound physiological 

 effects, probably from the rapid increase in osmotic pressure of 

 the constituent concerned in the cell after the saturation point 

 has been passed. Thus, although at two atmospheres of oxygen 

 pressure the amount of oxygen dissolved in corpuscles, plasma, 

 and tissue cells is not very appreciably higher than when the 

 oxygen pressure is about 100 mm., yet the activities of the cells 

 become affected and the animal dies in convulsions. So although 

 the uptake of potassium ion by the cell may not be appreciably 

 affected quantitatively when the concentration in the plasma 

 is increased compared to the uptake at a lower concentration, 

 yet the physiological action of the small additional amount upon 

 the cell may be enormous. 



It must be remembered that just as in the case of oxy- 

 haemoglobin there is no absolutely definite pressure which can be 

 spoken of as the dissociation point, but rather a short range of 

 pressure, during which association of the oxygen and haemoglobin 

 occurs, so in the case of other dissolved constituents (ions, organic 

 crystalloids, and anesthetics) and the tissue cells, there will 

 not be a sharp point, but a range of association with increasing 

 pressure, and the curve of osmotic pressure and association will 

 also vary with each dissolved constituent and each type of tissue 

 cell. 



In the case of every active drug, and every active constituent 



