12 THE LIVING WORLD. 



have been decided in the negative, but this only 

 shows that under certain conditions (which con- 

 ditions were doubtless not those of the times when 

 life first appeared) life cannot arise spontaneously. 

 They tell nothing as to indefinite unknown condi- 

 tions of the past. If they had been decided in the 

 affirmative, they could show only that life could 

 arise under certain conditions, which conditions 

 again were unquestionably not those of early times. 

 The experiments have all started with a nutrient 

 solution, which contained already products which 

 were the result of life, z.r., meat solutions, etc., arid 

 such a condition would of course have been impos- 

 sible at the time when life began. At best, then, the 

 experiments which have been performed upon spon- 

 taneous generations could serve only to make us a 

 little better acquainted with life and the conditions 

 under which it now acts, without helping us a step 

 toward answering the question of its primitive origin. 

 It cannot be denied, however, that if this subject 

 had been or ever shall be decided in the affirmative, 

 it would render the origin of life by natural laws 

 more probable, since it would show that living things 

 could come from the non-living, and this would be 

 one step toward the solution. 



2. Study of organic and physiological chemistry. 

 It may seem somewhat strange to count chemistry 

 as a source of biological history, and of course the 

 evidence it gives is only indirect. Chemistry has 

 been for some years now teaching us of the close 

 connection between chemical and biological laws. 

 It has shown that many organic bodies can be pro- 



