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 itis 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 
