THE PHYSIOLOGICAL PROBLEMS or TODAY 499 



(/-glucose, r/-mannose, and (/-galactose are fermentable, while 

 their stereoisomeres are not fermentable. But the influence 

 of the geometrical configuration goes farther. Voit has 

 suggested and Cremer has demonstrated that there is a far- 

 reaching parallelism between the fermentability and assimila- 

 tion of carbohydrates. Higher animals as well as yeast cells 

 are able to form glycogen from such carbohydrates as are 

 fermentable by yeast. The further development of these 

 stereochemical relations and their extension to proteids and 

 nucleins is another of the problems of physiology which will 

 contribute to the main problem, the analysis of the constitution 

 of living matter. I believe that the influence of stereochem- 

 istry will be more or less directly felt in many branches of 

 physiology, in questions of heredity, as well as in the theory 

 of space-sensations, as E. Mach has already intimated. 



In living organisms chemical energy is frequently trans- 

 formed into osmotic energy. Van 't HofFs theory of osmotic 

 pressure permits an application of the law of conservation of 

 energy to a class of phenomena to which this law was hith- 

 erto inapplicable, namely, the phenomena of growth, func- 

 tional adaptation, secretion, absorption, and even pathological 

 processes such as oedema. The physiologists who thought 

 that the blood-pressure determined secretion could not under- 

 stand why secretion took place under a higher pressure than 

 the blood-pressure. Comparative physiology shows that 

 secretion does not depend upon circulation, and the theory 

 of osmotic pressure indicates that the osmotic pressure in the 

 cells is more than twenty times as high as the blood-pressure. 

 The work of secretion is done by osmotic pressure and not 

 by blood-pressure. A prominent physiological chemist has 

 become a vitalist because he could not explain why the secre- 

 tions differ from the blood from which he thinks they are 

 formed. He overlooks among others the fact that the pro- 

 toplasm possesses the quality of semi-permeability, which 



