INTRODUCTION 7 



reactions, but only acts as the medium by which the 

 process is set going and also carried out. This in 

 itself, however, does not constitute the whole nature 

 of the mechanism designated by vitality. The mech- 

 anical actions, if they may be so called, are through- 

 out of the nature of a building up and breaking down 

 of complex molecular aggregations ; and essentially of 

 a dynamically unstable kind. This process of build- 

 ing up and of breaking down of such molecules is 

 called metabolism. It is not confined to ordinary 

 physiological processes, but in a gradually simplifying 

 scale, it is to be found even in many purely chemi- 

 cal and physical phenomena. It can be detected 

 even in some of the processes as manifested in 

 the phenomena of radio-activity. Nay, it is not 

 confined to these, for even in those phenomena in 

 which we should least expect it, it appears to be the 

 mechanism by which radiation in many cases, 

 as, for instance, luminosity is almost invariably accom- 

 plished. That the luminosity of flames and that of 

 phosphorescent and fluorescent bodies are of this 

 nature, due to the building up and breaking down of 

 such highly complex molecular agglomerations, though 

 much simpler than those of proteids, there is ample 

 reason from experimental evidence to think. In 

 other words, that these too are of the nature, and 

 come under the class of metabolic action, although, of 

 course, it is simpler than that which takes part in 

 living processes as familiarly understood. Still there 

 does exist the gradual simplification of such interaction 

 in Nature's scale of being ; and although we cannot go 



