CELLS AND TISSUES. 3$ 



in many ways to bear a reciprocal relation to each other 

 in the cell. The analysis of the colloidal material 

 decreases the former while it increases the latter, and 

 conversely. The metabolic changes which are forever 

 going on in the living organ compel us to look upon life 

 as a dynamic process, and the repeated attempts that 

 have been made to comprehend life physico-chemically 

 without taking this fact into consideration could not help 

 but seem inadequate. To discover the right connection 

 between this metabolic physiology and physical chemistry 

 is among the most important of the problems of general 

 vegetative physiology. 



IV. 



The biological significance of the crystalloids has until 

 recently been the main object of research with the 

 majority of those investigators who have made use of 

 physico-chemical methods in physiological questions. 

 Especially has use been made of the theory of solutions. 

 The great fertility of VAN'T HOFF'S teaching of osmotic 

 pressure had as an immediate consequence its unrestricted 

 application to all manner of life problems. The cells 

 were looked upon as liquid masses surrounded by semi- 

 permeable membranes which were supposed to act as 

 PFEFFER'S well-known model. A relative increase in the 

 osmotic pressure of the fluids surrounding the cells was 

 supposed to bring about a shrinkage, while an increase 

 in the osmotic pressure of the cell contents over that of 

 the -surrounding fluid was supposed to be followed by a 

 swelling of the cell. This so simple and consequently 

 so enticing conception of the role of osmotic pressure in the 

 organism meets, however, when further considered, with 



