ON PHYSICO-CHEMICAL METHODS AND PROBLEMS. i$ 



which until now could scarcely be explained, is an analogue 

 of the affinity existing between salts and proteins as dis- 

 cussed above. 



The way in which water and the way in which salt are 

 united with the colloids have many things in common, 

 for the water and salt mutually affect each other in the 

 organism, and each of the two is maintained at as constant 

 a value as possible. If we allow a swollen colloid to 

 desiccate in an atmosphere which is kept permanently 

 dry, we find that it loses water in a way analogous to 

 that in which a protein-salt mixture loses salt when 

 dialyzed against running water. In either case some 

 water or some salt remains behind which can be removed 

 only with the greatest difficulty if it can be removed 

 at all. The ion-protein compounds show a considerable 

 stability toward conditions influencing their state of 

 aggregation in yet another way. The presence of neutral 

 salts, for example, inhibits the effect of an acid or an alkali 

 upon the dissolved globulin, while non-ionized substances 

 do not do this. 



We must therefore look upon the ion- protein compounds 

 as being of importance in the animal body through 

 their ability to decrease its sensitiveness toward changes 

 in concentration, changes in temperature, and changes 

 in alkalinity. 



Through the decomposition of the large protein mole- 

 cules and certain carbohydrates there are produced 

 during metabolism substances having a low molecular 

 weight which in many ways have characteristics in 

 common with those of the salts, such, for example, 

 as urea or sugar. All these substances are either not 

 at all or only slightly ionized in water. They are there- 



