Relations and Transformations of Energy 43 



should be borne in mind that iron is an essential element for 

 the formation of chlorophyll, though probably it acts there 

 rather as a conductor of energy, or as an aid in energy trans- 

 formation. It is even possible that the purple and iron bac- 

 teria had an origin in common, and early evolved along diver- 

 ging lines, the former becoming in time the important and 

 advancing group, morphologically and physiologically. 



A comparison of the four groups now reviewed would suggest 

 that living substance very gradually originated amid chemically 

 acting and reacting inorganic compounds in aquatic or sub- 

 aquatic situations, and where colloid as well as crystalloid 

 bodies tended to arise through environal agency. From long- 

 continued interaction of emulsoid and suspensoid types of 

 colloid compound, a chemically sensitive and yet stable mixture 

 of several colloids resulted, that we now call protoplasm, which 

 as in Traube's cells threw off an investing wall. The most 

 important acti\dties of this mixture were surface chemical 

 interactions with surrounding liquid molecules; in time a utili- 

 zation of certain definite salts of these liquids, in part as a 

 constant source of constitutive or intra-molecular energy, and 

 in part as material for replacing broken down particles. Of 

 the four possible modes of accomplishing these two ends, the 

 one in which a definite compound became evolved by stages 

 to constitute chlorophyll proved physico-chemically the most 

 continuous, efficient, and beneficial in its relation. This then 

 became gradually selected and dominant among the colloid 

 masses or organisms that were to carry forward advancing 

 molecular aggregation, namely as green or chlorophylloid 

 plants. 



If we are to accept the concurrent views of physicists and 

 chemists, which call for a constantly increasing expenditure 

 of energy for the linking together of increasingly complex 

 molecules, then, for effecting such molecular combinations as 

 the formation of sugar, chlorophyll, or proteids, an enormously 

 high expenditure of thermo-electric energy, or a moderate 

 expenditure of some even more perfect and condensed energy, 

 seems absolutely called for as a physico-chemical necessity. 



