Introduction 7 



ing on our globe are such as to permit a re-creation 

 of life, or whether the necessary conditions were 

 presented once, and by a special sequence of events 

 such as we can never hope to reproduce. The par- 

 ticular combination of causes, to which the creation 

 of life was possibly due, may have existed only 

 as the earth cooled from its original incandescent 

 condition and perhaps thereby caused certain essen- 

 tial preliminary stages in the production of living 

 substance to arise." 



Protoplasm. All manifestations of life are di- 

 rectly associated with living protoplasm. When, 

 however, we attempt to define protoplasm we meet 

 with serious difficulties. We know that this viscid, 

 more or less granular matter, which constitutes the 

 living part of all cells, is an enormously complex 

 substance. Protoplasm is in no sense a definite 

 homogeneous chemical compound, but it is a mix- 

 ture of very many presumably heterogeneous units, 

 which in themselves may be of great complexity. 

 Of the real nature of the units making up the proto- 

 plasmic body of the cell we have very little certain 

 knowledge. Various names, " biophores," " gem- 

 mules," " micellae," etc., have been proposed for 

 these assumed units, but whatever may be their 

 structure, they lie far beyond the reach of our best 

 microscopes, and it will hardly be profitable here to 

 dwell upon the various theories that try to explain 

 the ultimate structure of the protoplasm. 



Any chemical analysis of protoplasm must be only 



