THE ORIGIN OF LIFE 29 



made their appearance upon the earth, and to those 

 working under the influence of this necessity the new 

 doctrine omne vivum ex vivo was not adequate. 



The primordial appearance of life is too important 

 a matter to be entirely neglected, so we are led to inquire 

 whether the simplest forms of life known to us are in any 

 sense primitive or whether they may not, in fact, be 

 highly developed compared to the primordial forms from 

 which they may have descended. 



Here we are confronted by several difficulties, one of 

 the chief of which is that our conception of "life" and of 

 " living substance" is based upon those forms with 

 which we are familiar, and whose manifestations we are 

 accustomed to describe as vital. It does not by any 

 means follow that only such are " alive," but it is only of 

 such that we speak as alive, and only such that we can 

 through the limitations of our conception of the term 

 prove to be so. 



It is also of some interest to inquire whether the phe- 

 nomena of life are so different from other chemical and 

 physical phenomena as to make us place the customary 

 gulf between the living and not living, or whether they 

 are not but a part of those universal phenomena by 

 which we can in a certain sense attribute life to the world, 

 to the solar system or to the universe itself! 



It is almost certain that life is no longer being gener- 

 ated, and that its original appearance upon this planet 

 took place under circumstances no longer existing. 

 Thus, conditions of temperature during past periods of 

 the world's evolution are believed by many to have 

 been responsible for molecular combinations impossible 

 at the present time. This is, however, conjectural, and 

 not demonstrable. The chief argument in its favor 

 is that all of our endeavors to see protoplasm come 

 into being independently of antecedent life, have failed. 

 We are thus obliged to conclude either that life never 

 did arise spontaneously, or that it can no longer be gen- 

 erated spontaneously, or that we are at present unable 



