Aridity and Evolution. 



219 



special conditions. Doubtless compounds of much greater in- 

 tricacy have been built up, but while we might make such sub- 

 stances, yet it would be extremely difficult for us to furnish the 

 supply of material and the continuance of conditions which would 

 permit this matter to exercise its initial functions to any appre- 

 ciable extent. The tests and criticisms which have been applied 

 to the results of the few essays that have been made for the pro- 

 duction of bodies which would be self-maintenant in a suitable 

 medium, have been for the most part misdirected. Thus in the 

 consideration of the hitheito unsuccessful efforts to produce 

 bodies simulating some of the properties of self-generating mat- 

 ter, tests for the physical and chemical properties of protoplasm 

 as well as for phenomena of the cell, have been applied, regardless 

 of the fact that the cell probably stands removed by a million 

 years of evolution from the simple living material which first 

 took shape, and represents, in fact, simply a successful form 

 of organism and by no means the only possible morphological 

 organization. 



PROPERTIES OF LIVING SUBSTANCE. 



After growth and decay, the next most important property of 

 living matter is that of irritability, of impressibli ty and ad- 

 justment to environment. The primitive substance of proto- 

 plasm endures because of a capacity for withstanding the current 

 range of temperature and insolation, and this endurance was 

 made possible by fairly automatic adjustments, one of the sim- 

 plest of which is encountered in recognizable form in living plants 

 today in the decrease of water content, which follows lower tem- 

 peratures acting upon protoplasm. Few adjustments are so 

 simple, and of course more complicated ones become possible 

 as atomic group after atomic group was added to the con- 

 stituency of living matter. 



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 those develop- 

 ing into plants and into animals. It seems probable that the 

 first specialization resulted from the formation of substances in 

 some of the living masses which converted radiations of certain 

 wave-lengths into heat and other forms of energy active in pro- 

 moting the reduction processes. The highest development of 



