A CHEMICAL SIGN OF LIFE. 1 



(From the Laboratory of Biochemistry and Pharmacology, The University of 

 Chicago; and Marine Biological Laboratory, Woods Hole, Mass.) 



SHIRO TASHIRO. 



From the earliest time to the present, our criterion of life has 

 been connected with the changes which are brought about by 

 death. The locomotive power of living matter is one of the 

 first things that disappears when it dies. Thus the idea of move- 

 ment erroneously led the simple minds of our ancestors to believe 

 that wind, fire, thunder and water had life. By close study of 

 the locomotion of living matter, however, we have gradually 

 traced this part of living phenomena to irritability of tissue 

 the property characteristic to living tissues only. This proto- 

 plasmic irritability is not only the potential of living matter, 

 to give rise to physical changes when a stimulus is applied 

 to it, but the fundamental and the only characteristic which is 

 common to all the living as long as they possess the power to 

 perform their own functions. And it is this property, according 

 to Professor Mathews, 2 that not only is the most probable point 

 of attack of natural selection but is also one of the main factors 

 which determines phylogenetic development of organisms. 



The presence of this irritable property in tissue the universal 

 sign of life cannot easily be determined in all living tissues. 

 The most common way of determining irritability is the physical 

 changes brought about by a stimulus. This physical change, 

 however, is not an unfailing indication of a response of the 

 tissue against stimulation. Several tissues in the animal, such 

 as nervous tissues, and an abundance of examples in the plant 

 kingdom, do not manifest at all any visible change, when stimu- 

 lated. Not only those living do not show such mechanical 



1 I wish to thank Dr. F. R. Lillie, through whose kindness I was occupying a 

 table in the Marine Biological Laboratory, Woods Hole, Mass., at the time when 

 the apparatus for these experiments was made. 



2 Mathews, Amer. Naturalist, XLVII., p. 94, 1913. 



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