8o BIOLOGICAL CHEMISTRY 



chloride which do not prevent haemolysis. Thus the assump- 

 tion is made that the cell wall is impermeable to the former 

 but permeable to the latter. 



The difference between such salts as potassium chloride and 

 ammonium chloride has been explained by the assumption 

 that it is the potassium ion to which the cell wall is imper- 

 meable, while the chlorine ion can pass through, but it may 

 possibly be due to a difference in the unionised salts. 



TABLE XVII 

 Showing types of substances that do and do not enter cells * 



Substances that do not seem Substances that enter cells Substances that do seem to enter 



to enter cells.) slowly. cells. 



Calcium, Strontium Amino acids Ammonia 



Barium, Magnesium Free Acids and Alka- 



Sugars (cane, grape lies, 



milk) Alcohols 



Aldehydes 

 Ketones 

 Urea 

 Bile salts. 



By comparing the substances that accumulate inside the 

 cells with the above table we see that so far as the organic 

 materials, except the sugars, are concerned they may enter 

 as simple diffusible molecules, be built up into complex 

 colloidal substances and thus removed from the active physico- 

 chemical system as described earlier in this chapter. 



In the case of the inorganic material we must look further 

 for the manner in which they have been accumulated. 



An accumulation, for instance, of potassium, might be 

 brought about by active cellular processes accompanied by an 

 expenditure of energy. After the accumulation has taken 

 place it might be maintained by the membrane becoming 

 impermeable or by a continual activity of the cell to maintain 

 the difference in concentration. 



On the other hand an accumulation may occur by some 

 means by which the ion in question is removed from the active 

 system so that there is an apparent increase in solubility. 

 This may take place in one of three ways. 



(1) The potassium may be adsorbed on the surface of some 

 colloidal particles. This is the way in which potassium is 

 supposed to be retained in the soil whilst sodium is washed 

 away in the drainage water. 



(2) The potassium may be precipitated as an insoluble 

 substance. 



(3) The potassium may form an unionised substance. 



* Selected from H. J. Hamburger, Osmotischer Druck, vol. I, p. 260. 



