6 A CHEMICAL SIGN OF LIFE 
way. The instrument which I have made to detect 
this carbon dioxide I have called a “‘biometer”’ because, 
as will be appreciated from this short discussion, it is 
an apparatus for measuring or detecting the amount of 
life possessed by different things. I shall show in the 
following pages that the increment of carbon dioxide 
produced by living things when they are irritated, or 
stimulated in any way, is a sure measure of the amount 
of life they have; and we may hope that it is to be an 
indirect measure of the amount of psychism they possess, 
although of course we cannot be sure of this as yet. It 
will be noticed that it is not the absolute amount of 
carbon dioxide which is the measure of life, but the 
increase above the usual production which occurs when 
a definite amount of stimulus is applied to the living 
thing, which is the real measure of life. Anesthetized 
or sick things do not show the normal increase; those 
abounding in life show a remarkable increase. 
The first results to be presented will be the proof that 
carbon dioxide production is the sign of life of a nerve 
fiber. And it will be well before going into this to say a 
few words about the scientific opinion concerning the 
nature of the nerve impulse generally prevailing before 
the work recorded here was done. 
The main function of a nerve fiber is to transmit a 
state of excitation from one place to another. It serves 
for the conduction of the nerve impulse, which it trans- 
mits in the most efficient manner. The nerve is also 
excitable at all points, since it can be stimulated by a 
variety of methods at any point along the fiber. When 
physiologists investigated what takes place in nerve 
fibers during the passage of nerve impulses, many 
