CONCLUSIONS 103 



most interesting problems of general physiology has been 

 to determine what is the nature of the irritable response 

 which living matter shows. It is this, the problem of 

 problems, which we wish to have solved. Is that 

 process physical or chemical? Is it simply an altera- 

 tion of permeability of membranes, as some have 

 supposed, or is it in reality in the nature of an explosion ? 

 Is the living thing essentially a bag of jelly with a 

 wonderful membrane about it, that membrane being so 

 wonderful that all the phenomena of life are to be 

 ascribed to its changes in state? For this is the view 

 which some maintain. They lead us to the holy of 

 holies of cells and tell us to behold a membrane ! Is life 

 nothing more than a membrane ? What kind of a subter- 

 fuge is this which we encounter ? All the riddles of life 

 are but the peculiar properties of a membrane! Upon 

 this membrane, as upon a magic carpet of Arabia, we 

 are invited to mount and travel over that unexplored 

 country whose mountain peaks shine in the distance. 

 Are we, then, beings of but two dimensions, nothing 

 but membranes, of which the magic proportions mock 

 us derisively, since we can never hope to seize that 

 which has but two dimensions? That such a view 

 resembles the membrane it has conjured up, in that it is 

 surface without depth, is self-evident. 



In no such simple and naive a manner can the un- 

 knowns in the equation of life be determined. For we 

 have found that everywhere, paralleling the irritability 

 changes in a perfect degree, as far as we have been able 

 to determine, go the chemical changes. Carbon dioxide, 

 that very simple substance, the last term in the katabo- 

 lism of living matter, rises and falls with irritability. 



