502 Mr. W. Stiles and Dr. F. Kidd. The Comparative 



In general, therefore, it may be concluded that earlier work agrees with 

 our own as to the relative degree of absorption of different ions. The 

 remarkable thing is that the differences between different tissues in this 

 respect are as small as they appear to be. 



In general it would appear that the initial rate of absorption of kations 

 is influenced very largely by the mobility of the ion or the coefficient of 

 diffusion of the salt. Troendle, on the contrary, draws the conclusion that 

 the rapidity of entrance of ions is not controlled by the force of diffusion 

 of ions and molecules through the protoplasm into the vacuole. He draws 

 this conclusion as a corollary to an earlier one which he reached, as we 

 think (12) on insufficient grounds, that the rapidity of entrance of ions is 

 independent of the concentration of the salt. We have already pointed out 

 how our own results as to the influence of concentration contradict the con- 

 clusion of Troendle as to the influence of concentration, although we agree 

 with him that the absorption of salt is not governed by Tick's law of 

 diffusion. Troendle concludes that the rapidity of penetration of salts 

 depends on the nature of the kation, and that the rapidity of entrance 

 increases with the atomic weight of the kation in any one group of the 

 periodic classification. This certainly appears to be the case with the alkali 

 metals, but Troendle admits that magnesium contradicts his rule, as be found 

 it was absorbed more rapidly than calcium. Our own numbers suggest 

 that calcium is absorbed more rapidly than magnesium at first, a fact which 

 would support Troendle's opinion, but how far this is a general phenomenon 

 remains to be seen. 



Troendle and earlier workers have not differentiated between the initial 

 rate of absorption and the position of equilibrium which is finally attained. 

 The results recorded in this paper show clearly that the initial order of 

 absorption is not maintained. Thus, calcium and sulphate, which are initially 

 absorbed at a rate equal to or greater than that of sodium and chloride 

 respectively, are absorbed ultimately to only a third or a quarter of the 

 extent to which these monovalent ions are taken in. How far this is a 

 distinguishing feature of divalent as contrasted with monovalent ions cannot 

 be said, although magnesium appears to behave like calcium. We know, 

 however, that the trivalent aluminium ion is absorbed to a large extent, but 

 this may be to a considerable extent, as Meurer supposes, by the cell wall and 

 not by the cell interior, and so may be an exceptional case. 



We would conclude, tentatively, that the initial rate of absorption of salts 

 is dependent to a great extent on the mobility of the ions or the coefficient of 

 diffusion of the salt, but that the total intake of salt depends on something 

 other than this, as a result of which calcium, magnesium, and sulphate are 



