ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 273 



neously (for example, succinic acid to a mixture of equal parts 

 of water and ether) the proportion of this substance found 

 in solution in each of the solvents will always be the same no 

 matter how much of the substance is offered the two solvents. 

 This means that if of six grams of succinic acid offered a 

 certain volume of ether and water, five grams are found to 

 dissolve in the ether and one in the water, then if twelve grams 

 be offered the two solvents, ten will dissolve in the ether and 

 two in the water. The proportion of 5 : 1 is therefore main- 

 tained. 1 



With these ideas in mind it is only necessary to reexamine 

 the list of substances which experiment has shown enter 

 cells more or less rapidly and see if they are not all of 

 a character which are more soluble in ethereal or oily sub- 

 stances than in water, and that those which stand first in the 

 list and consequently enter cells most rapidly are not such 

 as have the highest distribution coefficients. An illustration 

 may make this clearer. The repeated substitution of an 

 atom or a group of atoms for some other atom or group of 

 atoms in a chemical compound is often accompanied by 

 marked changes in the solubility of this compound and its 

 derivatives. Glycerine enters a cell only very slowly. When 

 an atom of chlorine is introduced into this compound it 

 enters protoplasm more rapidly, and when two are introduced 

 still more rapidly, for these derivatives are more readily 

 soluble in fats than the original glycerine. The same holds 

 true of urea and its methylated derivatives. While urea 

 diffuses but slowly into cells, the introduction of one, two, 

 or three methyl radicles into this compound increases pro- 

 gressively its solubility in fats and hence the rate of diffusion 

 into living cells. 



Having shown that the entrance of many different sub- 

 stances into cells is dependent upon their solubility in fat- 

 like bodies we may ask more specifically, What are these 



'SeeHoBER: I.e., p. Ill, 



