366 Sir W. Thiselton-Dyer. On the Influence of 



are not in themselves, in any intelligible sense, living though essential 

 to the exhibition of vital phenomena. 



There our analysis of living matter by physical methods for the 

 present stops. But we are justified in pushing, at any rate, semi- 

 physical conceptions as far as we dare. We conceive, therefore, the 

 physical constituent molecules of protoplasm as aggregated into larger 

 molecules which, as they are unlike anything we know as purely 

 physical, we call physiological.* Of the properties of such molecules 

 we have some faint conceptions. The first is their instability. They 

 are kinetic ; " living substance is continually breaking down into 

 simpler bodies, with a setting free of energy ; on the other hand living 

 substance is continually building itself up, embodying energy into 

 itself, and so replenishing its store of energy." f This kinetic condi- 

 tion is essentially life ; when it ceases, we have hitherto believed that 

 the constituents of protoplasm come under the sway of purely inorganic 

 conditions. 



If we pause for a moment to attempt a quasi-mechanical explana- 

 tion of the more developed phenomena of living organisms, such for 

 example as are included under heredity, we are led to suppose that 

 the physiological molecules may themselves be grouped into larger 

 aggregates. And each stage of aggregation introduces us into a new 

 order of phenomena. All that we can say is, that beyond the first 

 stage the properties which are characteristic of higher molecular aggre- 

 gates, are ultra-physical, taking physical in its ordinary signification. 

 That does not imply, however, that physical conditions are ever in 

 abeyance. Each stage of aggregation is conditioned by every one that 

 precedes it. In this sense life rests au fond on a physical basis. 



A continuous kinetic condition appears to be one distinctive pro- 

 perty of physiological molecules. This not merely manifests itself in 

 continuous chemical activity, but under appropriate conditions in actual 

 visible motion. And it is to be remarked of the former, that though 

 chemical in kind, it is undoubtedly ultra-chemical as chemistry is under- 

 stood in the laboratory. A further characteristic of the physiological 

 molecule is that it possesses the power of breaking up chemical combi- 

 nations and reuniting their constituents in a way which absolutely 

 eludes the methods available to the chemist, and entirely outstrides 

 the pace at which he can proceed. There is the same kind of difference 

 between the two methods as there is between arithmetic and the cal- 

 culus in the solution of a mathematical problem. 



The question then is, how far the effects of Professor Dewar's experi- 

 ments and of those who have preceded him in the same field, require 

 us to modify our conception of the physiological molecule. Are we 



* Identical with Foster's " scmacula," ' Text-book of Physiology,' Part I, 5th ed., 

 p. 6. 



t Foster, loc. ext., p. 41. 



