METABOLISM AND THE DISTRIBUTION OF MATERIAL 237 



cell is a monstrosity, for how does it explain the entry of food and the 

 exit of metabolic products (metabolites) from the cell. If the mem- 

 brane is permeable for these, the osmotically active crystalloids 

 cannot induce transfer of water. All variations in volume of blood 

 corpuscles, spermatozoa, plant cells, etc., produced by electrolytes 

 and attributed to osmotic pressure up to now, are just as well ex- 

 plained by swelling and shrinking. Gels swell up in water, acids and 

 alkalies; salts on the other hand, hinder swelling and cause shrinkage. 

 Moreover, new, purely physico-chemical observations likewise warn 

 us to employ great caution in our consideration of osmotic processes 

 in the organism. Much more substance may be dissolved in the in- 

 terior of the cell than in its surrounding fluid without the osmotic 

 pressure making this evident. We saw on pages 46 and 47 that 

 with decrease in the surrounding osmotic pressure, the osmotic 

 pressure in a cell with a permeable membrane containing colloid, 

 falls, although if reckoned according to the salt content, the osmotic 

 pressure should have increased. These findings of W. BILTZ and A. 

 VON VEGESACK* necessitate a revision of all former conclusions 

 derived from the observation of osmosis in cells. 



Circulation of Water in Animals. 



A movement of water results when conditions arise which change 

 the relative swelling of the organs. When subjected to high tem- 

 perature or after violent exercise, etc., the skin loses water, the 

 blood loses water through the lungs, which causes a flow of water 

 from the other organs. Conversely, an excess of water from the in- 

 testines, or in the case of frogs and certain other animals from the 

 skin, is transferred to other organs and re-excreted by the kidneys. 

 Other circumstances may arise, however, which determine the cir- 

 culation of water: concentration of acid in a tissue increases its 

 swelling capacity, attracting water, e.g., in. venous blood or an edema, 

 whereas simultaneous salt formation leads to a shrinking or loss of 

 water. 1 In circumstances in which osmotic pressure may become 

 active, as when a membrane is interposed, the change of a colloidal 

 substance into a crystalloid under the influence of enzymes may effect 

 a transfer of water; the water flows to the place where the osmotic 

 pressure is higher. We shall return to the details of this question 

 when we consider the individual organs. 



1 From this it results that the presence of colloids regulates the movement of 

 water in an entirely different and at times in a direction opposite to that of the 

 osmotic pressure: Acid + salt, as a result of the higher osmotic pressure, should 

 increase the amount of water attracted; in the case of colloid structures, how- 

 ever, they decrease it, since salts abolish to a greater or less extent the swelling 

 action of acids. 



