THE ORIGIN OF LIFE 23 



the paper he substituted fine gauze through which the odor of the 

 meat could rise. Over it the flies buzzed, and upon it they laid 

 their eggs, but the meshes being too small to permit the eggs to 

 fall through, no maggots generated in the meat, they were, on 

 the contrary, hatched on the gauze. By such a series of experi- 

 ments Redi destroyed the belief in the spontaneous generation of 

 maggots in meat and with it many related beliefs." 



But in 1683 a new phase of the subject was opened by 

 the discovery of bacteria and many other minute forms 

 of life by Leeuwenhoek, and many scientific men to 

 whom the spontaneous generation of fishes, frogs, or 

 insects appeared to be an absurdity, were misled into 

 believing that what was not possible for these highly 

 organized animals might easily take place among such 

 minute and lowly organized beings as those of the new 

 world disclosed by the microscope. It seemed as if the 

 threshold of life had been reached. 



To the intelligent mind of the present day, disem- 

 barrassed of erroneous beliefs, it will at once appear that 

 the size of the creatures has no influence upon the merits 

 of the case, for there are minute organisms visible only 

 to the microscope that are as complexly formed as others 

 that may be inches or even feet in length. To the idea 

 of simplicity of structure the mind may yield; it does at 

 first seem more reasonable that an organism of extreme 

 simplicity might arise spontaneously than that one of 

 great complexity could do so. 



So it seemed to these early scientists. The micro- 

 scopic organisms were small, and in many cases of no 

 visible complexity, and with few exceptions they seemed 

 satisfied to believe that they arose de novo. So, in the 

 nineteenth century we find the same convictions regarding 

 the spontaneous generation of the slightly known forms 

 of microscopic life that had been held hundreds of years 

 before regarding the slightly familiar small but complex 

 animals, and thousands of years before regarding all 

 living beings. 



But as time went on the world of microscopic life was 



