INTRODUCTION. 9 



This means, that if the complete history of the earth 

 couldbecompressed into)acourse 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, Uving 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 Ufe was impossible 

 upon it. 

 2dly. because we know that no other elements occur 

 in the Hving beings than in non-Uving nature, 

 so that both are composed of the same substan- 

 ces. 

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

 the majority of plants is able to transform large 

 quantities of inorganic matter into hving 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 Uving substance, once pre- 

 sent in the seed which sprouted to form the 

 poplar. 

 Where we thus find that all bodies on earth, Uving 

 as weU as non-Uving ones, are built up by the same ele- 

 ments, where we know furthermore that these very 



