640 THE MECHANISM OF ABSORPTION 



Of the factors involved in Hamburger's scheme of absorption, the 

 only ones which could be influenced by change in the solution 

 to be absorbed would be either molecular imbibition or diffusion 

 depending on differences in diffusion velocity or in the perme- 

 ability of the cells to the substance in solution. Molecular im- 

 bibition is influenced by salts ; for Hofmeister found that 

 gelatine plates absorbed less water when soaked in a sulphate, 

 tartrate, or citrate than in a chloride, bromide, or nitrate. But 

 considering the uncertainty how far living tissues show molecular 

 imbibition at all, much stress cannot be laid on Hofmeister's 

 observation. He also showed that the same division of anions in- 

 dicated the relative power of different salts to precipitate egg 

 albumin or gelatine ; and in this way there might exist some 

 general relation between the power of salts to precipitate colloids 

 and to pass into living cells. But this is not the case. For 

 Leathes and Starling found that the pleural endothelium absorb 

 solutions of MgS0 4 or Na 2 S0 4 just as rapidly as those of NaCl ; 

 and we have already seen that the relative permeability of red 

 blood-corpuscles to salts is not the same as the relative rates 

 at which the same ions are absorbed from the intestine. 



Hober has put forward an explanation founded on the ob- 

 servation that with few exceptions a parallelism exists between 

 the diffusion velocity of a crystalloid and its rate of absorption 

 from the gut. From this it would follow that the epithelium 

 acted like an indifferent membrane ; but the exceptions to the 

 rule are sufficient to show that this cannot be the case. The 

 more important exceptions are, in the first place, dextrose, cane- 

 sugar, galactose, and urea, which are absorbed more rapidly than 

 corresponds to their diffusion velocities. In the case of the 

 sugar, the certainty that ferment action takes place during ab- 

 sorption introduces an unknown factor which may or may not 

 explain the discrepancy. Hober gave an explanation for urea 

 which will be referred to later. The second important group is 

 formed by chlorides, bromides, and iodides, which have practically 

 the same diffusion velocities, and yet show decreasing rates of 

 absorption in the order named. Finally, there came the fluorides 

 and oxalates, and salts of arsenic and quinine, all of which 

 damage the epithelium, and are absorbed more slowly than would 

 be expected from their diffusion velocities. 



Wallace &nd Cushny made a different suggestion, namely, 



