A CHEMICAL SIGN OF LIFE. 283 



changes while functioning, but several non-living matters 

 constantly undergo physical changes when disturbed by external 

 conditions. Therefore it has been customary for the biologist 

 to decide whether or not matter is living by several other ac- 

 companying changes during the performance of a function. 

 Such changes have been measured by rise of temperature, pro- 

 duction of CO 2 , histological variation before and after the 

 stimulation, and electrical response. None of these functional 

 changes when taken individually can be considered as a specific 

 sign of life. 



Although Herzen claims that under certain conditions of local 

 narcosis, the nerve fiber may give an action current although no 

 muscular contraction follows, and O. B. Ellison recently demon- 

 strated by the use of cinchonamine hydrochloride the absence of 

 negative variation without abolishing excitability, yet according 

 to Waller the presence of life can be demonstrated by an electrical 

 change. In his admirable book on the "Signs of Life," 1 he 

 states that chemical change is a sign of life and an electrical 

 change is a sign of a chemical change; therefore the electrical 

 change is the sign of life. It is very interesting to note in the 

 case of a dry seed, he could measure equally well quantitatively 

 the different electrical changes according to the different ages 

 which characterize the different degrees of vitality of the seed, 

 in spite of the fact that he could not detect any chemical 

 change which usually produces CO?. He concludes, however, 

 that it Is possible, or rather certain that our method of chemical 

 investigation is not refined enough to reveal to us the smallest 

 and most infinitesimal change that may be going on in apparently 

 dry or dormant seed. It was this conclusion of his that sug- 

 gested to me the desire to make an inquiry to ascertain whether 

 or not I could find some new method by which an easy sign of 

 life may be observed. 



When I had constructed a new apparatus, 2 which can detect 

 COa as small as o.ooooooi gram, the measurement of irritability 

 became much simpler, for with it we established a few new facts 

 which deal with the fundamental nature of protoplasmic irrita- 

 bility. The idea that irritability in general is closely associated 



1 Waller, "Signs of Life," New York. 



2 Am. J. of Physiol., XXXII, p. 137, 1913. 



