INTRODUCTION. 9 



This means, that if the complete history of the earth 

 couldbe compressed intoacourse of daily one-hour lectu- 

 res lasting one and a half year, the life of a student — 

 suppose he could begin attending them immediately 

 after birth and continue to do so up to the comple- 

 tion of his 8oth year — would be just sufficient to 

 hear two seconds of these lectures. 



Once — or repeatedly — during this long, long pe- 

 riod, living beings arose from much more complicated 

 combinations of the elements also. 



Keen as this deduction may seem to be, in the face 

 of the fact that generatio aequivoca has never yet been 

 demonstrated, we are nevertheless forced to it. 

 istly. because there has been a time in the history of 

 the earth, during which life was impossible 

 upon it. 

 2dly. because we know that no other elements occur 

 in the living beings than in non-living nature, 

 so that both are composed of the same substan- 

 ces. 

 3dly. because we know that even at the present time, 

 the majority of plants is able to transform large 

 quantities of inorganic matter into living one. So 

 we know f . i. that the whole body of a poplar is 

 formed of inorganic matter, thus transformed 

 by the wee little bit of living substance, once pre- 

 sent in the seed which sprouted to» form the 

 poplar. 

 Where we thus find that all bodies on earth, living 

 as well as non-living ones, are built up by the same ele- 

 ments, where we know furthermore that these very 



