320 



COLLOIDS IN BIOLOGY AND MEDICINE 



From this we see that sodium chlorid absorption is greatest in 

 the presence of urea, because, in spite of the great shrinkage in the 

 quantity of fluid, the concentration of sodium chlorid is but slightly 

 increased. This coincides with the results of the experiments of 

 H. BECHHOLD and J. ZIEGLER * 2 in which urea in the main favors 

 diffusion in gelatin and in jellies. If we assign to acetone properties 

 similar to alcohol, we may explain the surprisingly rapid absorption 

 of water in the above experiment, because, as has been said on page 

 70, a certain proportion of alcohol increases the ability of glue to 

 swell. From these observations we gather new points of view in 

 regard to the ready absorption of protein cleavage products, which I 

 shall elaborate on page 411. 



We may make still further deductions from the above observations, 

 since in experiment 1 we have seen that the NaCl content of the 

 blood is higher (about 0.6 per cent); so that it has been absorbed 

 against the osmotic pressure of NaCl in the intestines. This is ex- 

 plained on pages 318 and 319. In experiment 2, the contrary is 

 the case: the osmotic pressure is higher than in the blood; appar- 

 ently the structures capable of swelling absorb less NaCl in the 

 presence of acetone. 



Nor need we be surprised by the fact discovered by OTTO COHN- 

 HEIM, that a hypotonic grape sugar solution introduced into a loop 

 of the small intestine becomes more concentrated. From the same 

 experiments we know that grape sugar, which of itself diffuses slowly, 

 decreases the permeability of the swollen jelly, and thus blocks its 

 own passage. 



Substances which themselves possess great capacity to swell, e.g., 

 agar, hinder the absorption of water to a high degree. 



It still remains a question, how the intestine maintains its ability 

 to take up water, since water is constantly being removed from the 

 intestine by diffusion or swelling. The theory proposed by MARTIN 

 H. FISCHER * seems to offer valuable assistance. 



He starts with the idea that venous blood containing carbonic 

 acid has a tendency to swell, i.e., to take up water; arterial blood, on 



