FROM THE SMALL INTESTINE 641 



that the permeability of the intestinal epithelium to various 

 anions was related to the solubility of their calcium salts. They 

 believed that the precipitation of an insoluble calcium salt in 

 the epithelium would retard absorption. The main evidence 

 against the view is the fact pointed out by them, that the relation 

 between solubility of the calcium salt of an anion and its ab- 

 sorption rate is not absolute. The same view has been put 

 forward to account for the power of many salts with a poly- 

 valent anion, like citrate and oxalate, to stimulate nerve and 

 muscle. It is supposed that these salts act, not by means of 

 the many negative changes which they possess, but by precipi- 

 tating the calcium in the tissues, and so neutralising the depressing 

 action of the calcium salts. Although there exists a general 

 parallelism between the stimulating power of anions and the 

 insolubility of their calcium compounds, there are too many ex- 

 ceptions to make it likely that the one property is the cause of 

 the other. We have seen that the stimulating power of an 

 anion is determined by its solution tension, and it is probable 

 that the same factor helps to determine its power of precipitating 

 calcium. These considerations point to the idea that the rate 

 of absorption of different anions might be related to their ionic 

 potential. Our knowledge of the solution tension of anions is 

 very imperfect ; but to some extent their rate of absorption is 

 related to their solution tension in such a way that anions with 

 the lowest solution tensions, which are therefore the most 

 physiologically active or toxic, are the least rapidly absorbed. 

 In the case of cations the relation between rate of absorption 

 and solution tension is much closer. The relation is such that 

 cations with the highest solution tension, which are consequently 

 least depressant, are the most rapidly absorbed. Such facts 

 suggest that the factor which determines the rate at which a 

 salt is absorbed, is the sum of the physiological actions of its 

 ions. Until we understand more of ionic action upon bioplasm 

 generally it is idle to speculate upon the nature of the action of 

 ions upon the properties of the intestinal epithelium. And we 

 are not in a position at the present moment to say whether the 

 rate of absorption of an electrolyte is determined by vital action 

 or not. 



From what has been said it is clear that the slow absorption 

 of a salt might be due to its anion alone, e.g. sodium sulphate, 



2s 



