II. INTKODUCTION. 11 



living beings, indicate the contemporaneous existence of the more complex as well 

 as the simplest of organic forms ; but, nevertheless, life may have been ushered 

 upon earth, through oceans of the lovrest types, long previously to the deposit of 

 the oldest paljEozoic rocks as known to us ! ! 



The primitive species of living beings which appeared upon earth, and those 

 which have been successively and periodically produced, must have been the result 

 of pre-existing natural conditions, or the former alone originated in this manner, 

 and the latter were the result of their transmutation under the influence of vary- 

 ing exterior conditions, or all species in all times originated directly through supra- 

 natural agency. 



The last mode, of course, can only be an inference, in absence of all other 

 facts ; and if living beings did not originate in this way, it follows they are the 

 result of natural conditions. 



Be this as it may, the most prolonged and closest observations, and the most 

 carefully conducted experiments have not led to the proof of a -single instance of 

 spontaneous or equivocal generation even of one of the simplest of all living beings ; 

 but, on the contrary, they all lead farther and farther from or entirely disprove it, 

 and thus involve the whole subject in obscurity. 



Schulze^ performed an experiment to test the possibility of equivocal generation 

 under the play of the indispensable conditions of life, free from access to any pre- 

 existing vegetable or animal germs. 



A glass vessel half filled with a mixture of various dead vegetable and animal 

 substances in water, was heated to 212° F., so as to destroy any living bodies which 

 might exist within. To the vessel was then adapted a pair of Liebig's bulbs, one 

 of which contained sulphuric acid, the other a solution of potassa, and through 

 these only could the exterior air have access to its interior. The apparatus was 

 then placed in a window, where it received the full influence of light and the 

 necessary temperature for the production of life. The air within the vessel was 

 daily renewed from May until August, by blowing through the sulphuric acid, from 

 which it could suffer no change, except to be deprived of moisture and organic 

 particles. During all that time, not even the simplest animal or vegetable forms 

 were produced, while in an open vessel containing the same mixture, in the same 

 situation, there were observed on the following day numerous Vibrios and Monades, 

 and to these were soon added larger animalculae. 



This interesting experiment of Schulze, I repeated with three different vessels ; 

 in one of which was a mixture of ditch-mud and confervae with water ; in a second, 

 decaying wood with water ; and, in the third, a clod of earth with growing grass, 

 earth-worms, and water. Exactly under the same circumstances, they were sup- 

 plied with fresh air from time to time, from July of 1850 to December of 1851, and 

 in the end the results were the same as in the experiment of Schulze. 



These experiments, however, may not be conclusive ; other conditions may be 



^ Notice of the Kesult of an Experimental Observation made regarding Equivocal Generation. By F. 

 Schulze, Berlin. The Edinburgh New Philosophical Journal, vol. xxiii. 1837, p. 165. 



