THE G EXES IS OF LIFE. 159 



to ensure their favourable reception. Animals and plants, 

 as far as everyday experience could discern, were in no case 

 propagated de noi'o, but sprang invariably from living prede- 

 cessors. The old maxim, Ex nihilo nihilfit, expresses after 

 all a very just conception of the order of nature at large; 

 and, in its application to living things, the aphorism might 

 well be paralleled by Redi's assertion that nothing living 

 could arise from a dead or inorganic source. 



As time passed, however, the microscope was being 

 perfected. From the days of simple magnifiers to those of 

 compound microscopes, the optician's art slowly but surely 

 progressed. Leuwenhoeck, the Dutch naturalist, for ex- 

 ample, attained great excellence in the art of grinding 

 microscope-glasses, and as a result of perfection in this art 

 was enabled to discern in 1702 the first rotifers, or "wheel 

 animalcules," in the rain-water which had collected in a gutter 

 on his house-top. Lower forms of life, unknown in Redi's 

 day, animalcules of a size which, for minuteness, were un- 

 dreamt of in the seventeenth century, were thus brought to 

 light during the eighteenth ; and such discoveries in animal- 

 cular life naturally came to possess a very distinct and 

 important bearing on the subject of the origin of life at 

 large. Philosophers in the eighteenth century smiled at the 

 credulousness of their predecessors, who believed in the 

 " spontaneous generation " of animals of such highly organ- 

 ised nature as flesh-flies, gall-flies, and other insects. But the 

 origin of the living specks collectively named " animalcules" 

 was a matter which assumed an entirely different aspect. 

 The animalcule might possibly be propagated in ways 'and 

 fashions impossible to the higher insect. The rule of life 

 and development for the highly organised being might prove 

 to be utterly different from that regulating the genesis of 

 the animalcule. Hence the scientists of the eighteenth 

 century, finding new materials to work upon in the fields 

 of life which the microscope had revealed, were led to 

 attempt anew the solution of the problem to which Redi 

 had apparently given an exhaustive answer. Driven from 



