president's address — SECTION D. 115 



in matter for temporary purposes, and, these fulfilled, quitting it for 

 another phase of existence. Such terms as "vital principle," 

 " organising agent," in the sense of a presiding genius regulating 

 bodily functions, have become almost obsolete in biological litera- 

 ture ; the generation which from a scientific standpoint upheld the 

 hypothesis of its existence has well nigh passed away, and left to 

 the conservatism of popular sentiment the struggle against the 

 logic of fact. But though it is perfectly clear to most physiologists 

 that life is not an embodiment of anything at any time external to 

 the body, wh?t it actually is, is less unanimously decided upon by 

 them. By many it is defined to be " the sum of the actions of an 

 organised being;" others, very properly objecting that the actions 

 of an organised being cannot of themselves constitute its life, prefer 

 as a definition •' the state of the actions peculiar to an organised 

 being," and an improvement on this again is made by those who say 

 it is '• the condition of activity manifested by such beings." The 

 defect in all these renderings seems to be the imcertainty attaching 

 to the unqualified use of the terms " action " and " activity," a defect 

 which may perhaps be remedied by defining life as " the molecular 

 activities peculiar to organic structure." It is the consequence of 

 the formation of a substance susceptible of organisation under the 

 impress of that mode of intramolecular motion. Its prime pheno- 

 mena are irritability — aptness for automatic motion in mass in 

 response to stimtili, and metabolism — the faculty of converting 

 irritants of a suitable kind into nutrients, suitability being deter- 

 mined by elective means akin to if not identical with chemical 

 affinity. The molecular activity in wdiich life consists is the 

 ultimate fact in this direction, and must remain so until the time is 

 ripe for resolving ail modes of energy into one. So far as this 

 peculiar activity produces pecidiar effects, life mtist for the present 

 be held distinct from those energies which are incapable of bring- 

 ing them about. On the other hand the production of phenomena 

 identical wdth those which are characteristic effects of the physical 

 energies warns us against the assumption that life has in its nature 

 nothing in common with them. The molecidar activity — life — is 

 apparently convertible into the other molecular activities; the work 

 done by the contracting muscle-fibre appears partly as heat, partly 

 as electricity, that of other tissues as light, of others as chemical 

 synthesis or analysis. Were the question between any two of 

 these physical forms of energy, such convertibility would be held 

 to indicate mutual relationship, and though no one of the latter is, 

 so far as we know, convertible into life, this is hardly sufficient 

 grotmd for regarding the organising activity as essentially different 

 from the non-organising. 



Seeing that the operations of ordinary chemism within the body 

 are directed and controlled by vitality, and are at the same time 

 necessary to the continuance of vitality, it is conceivable that life 

 is a concurrence of the two modes of molecular activity mutually 



