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282 D. T. MACDOUGAL 



adjustments are so simple, and, of course, more complicated ones 

 became possible as atomic group after atomic group was added to 

 the constituency of living matter. 



Along with these acquisitions the feature of the rhythmic action 

 which has become so characteristic and important for the living 

 growth is to be considered, and this with contractility is dependent 

 upon surface tension, viscosity, etc. 



So far the properties suggested are those common to all living 

 forms, but there must have ensued many differentiations of living 

 matter, of which we have two survivals in plants and in animals. It 

 seems probable that the first specialization resulted from the forma- 

 tion of substances in some of the living masses which converted radia- 

 tions of certain wave-lengths into heat and other forms of energy 

 active in promoting the reduction processes. A fortuitous move- 

 ment toward such specialization may indeed have been the factor 

 that made for survival in an environment of decreasingly avail- 

 able supply of chemical energy. The highest development of this 

 power of absorption of light rays is to be assigned to chlorophyll, 

 but preceding the formation of this very intricate and unstable sub- 

 stance there may have occurred a series of other compounds acting 

 as heat-absorbent screens, of which the reddish and bluish pigments 

 of the lower algae are surviving examples. Many disintegration 

 products constituting the reds and blues of plant tissues sustain 

 physical relations of a similar character to sunlight. 



It is not possible to formulate any rational conception of living mat- 

 ter without including its environmental relations. These become of 

 the utmost importance at the moment of formation of self-generating 

 matter, and it may be assumed with perfect safety that of all the pos- 

 sible synthetic processes only those which ensued in the presence of a 

 medium which furnished substances suitable for building material 

 could survive. Furthermore, when the accumulation of this material 

 and its specialization is considered it is apparent that successful 

 origination occurred only on solid or semi-solid substrata rather than 

 in undifferentiated solutions in open waters. Still an abundance of 

 this liquid would be of great importance to the colloidal masses which 

 we may think of as the earliest living things, and, as will be shown 

 presently, water has continued to be the most important of all of 



