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 



