IRRITABILITY AS A SIGN OF LIFE 3 



we possess. Thus a part of the study which follows has 

 been made upon such simple things as seeds and garden 

 peas. It is surprising how closely the results obtained 

 with these parallel those obtained from nerves. 



The really important and peculiar property of living 

 things is the psychic life they show. And if we actually 

 had an accurate means of testing the degree or amount 

 of life, it would be some kind of a reagent or instrument 

 for testing "psychism," as we may call it. But un- 

 fortunately we cannot at present find any means of test- 

 ing this property. We do not know what its physical 

 basis is, and, until we discover that, we cannot make 

 a psychometer which we can apply to all kinds of 

 living and non-living things, and thus measure the 

 amount of psychism, and hence of life, which they 

 possess. In the absence of any such psychometer we 

 have to do the best we can, and take as a measure of 

 this property those physical and chemical changes which 

 experience or experiment demonstrates to us always 

 accompany the psychic change. The situation is very 

 much as it was in the realm of electricity before the 

 galvanometer was invented; an idea of the quantity 

 of electricity produced by a battery could be obtained 

 only indirectly by measuring the amount of chemical 

 change which the current produced, since Faraday 

 found that that amount was always a measure of the 

 amount of electricity. 



There are material changes which occur in living 

 things as long as they are alive and show psychic life 

 of any kind. The changes which we may rely upon to 

 measure the amount of life, and thus indirectly the 

 amount of psychism, are partly visible changes, but in 



