104 A CHEMICAL SIGN OF LIFE 



Function without chemical change has been found no- 

 where. Respiration, or at least this phase of respira- 

 tion, and irritability are in some way bound up together, 

 and we many now very briefly ask ourselves how they 

 may be related. 



The connection between irritability and metabolism. 

 What, then, is the connection between the irritable and 

 the respiratory process? Could we answer this ques- 

 tion we should have solved one of the most fundamental 

 of all questions of science. However, we do not hope 

 to be able to answer it at present. But let us at least 

 see what facts we can discover. The first of these facts 

 which strikes us is that living matter, even when it is 

 not stimulated, continues to give off carbon dioxide 

 and to respire. What is the significance of this fact? 

 Why should this constant consumption of material go 

 on in the absence of outside work to do ? The main 

 function of the resting metabolism is to keep the tissue 

 irritable. As long as a tissue remains living and irritable 

 we find it to be the seat of production of carbon dioxide. 

 To be sure, it continues sometimes to give off carbon 

 dioxide after death, but it never ceases to do so as long 

 as it is alive. After death the rate, with possibly a tem- 

 porary increase, soon diminishes. For nothing is more 

 certain than that living matter burns up faster than 

 the same matter after death. Death extinguishes the 

 torch of life, although it may continue to smoulder for a 

 time when the spirit of its flame is gone. 



Does not this fact mean that life, or rather the living 

 state, is a dynamic rather than a static phenomenon ? 

 We might conceive the living matter as a very highly 

 explosive substance, very unstable and ready to go to 



