Developmental History of Infusorial, Animal Life. 357 



Do we not constantly see vegetable mould covering our cheese, 

 our jam, our bread ? Even our air-tight vessels cannot be 

 kept free from plants and animals, where neither plant nor 

 animal could be seen before, and where it appears impossible 

 that their seeds could have penetrated. Where do those para- 

 sitic animals come from which are to be found in the blood, 

 the brain, the liver, and the eye ? How got they there ? These 

 questions are more easily answered on the supposition that 

 generation can take place spontaneously; nevertheless, the 

 weight of scientific evidence has been year after year accumu- 

 lating against such a supposition, and the majority of physiolo- 

 gists have come to the positive conclusion that no generation 

 whatever can occur except by direct parentage.* 



And yet how difficult at times to divest the mind altogether 

 of some such theory, when asked to account for the apparently 

 sudden appearance in a most unlikely place, of some such ex- 

 traordinary creature as that of Mr. Crosse's acarus. This, as 

 you are aware, was found in a solution of silicate of potash, 

 through which an electric current was passing, and after 

 every care had apparently been taken to free the apparatus from 

 every particle of dust and foreign matter ; or that noticed by Dr. 

 Maddox on the surface of a nitrate of silver bath, which had 

 been set by for some time. The several bright spots in motion 

 proved to be well-developed, highly- organized acari, looking 

 like "miniature fat sheep." f 



These, and other like remarkable instances were at one 

 time regarded as good evidences of spontaneous generation, 

 and afforded a simple and easy mode of getting rid of a 

 difficulty. 



The first formidable assailant of the doctrine of spontaneous 

 generation was the celebrated Italian naturalist, Redi. In his 

 work On the Generation of Insects, he proved that the worms 

 and insects which appear in decaying substances, are really 

 developed from eggs designedly deposited there by the mature 

 animal. But it was thought preposterous to suppose that 

 putrefaction could produce an insect, and this explanation was 

 for a time rejected. But driven from the insect world, where 

 such an hypothesis could have no chance of success, the up- 

 holders of it sought refuge in the world of infusorial and 

 parasitic life. 



Any one acquainted with the writings of Leuwenhoek will 

 see how steadily this father of microscopy set his face against 

 spontaneous generation, because even his imperfect instrument 

 showed him that many of the most minute animals produced 

 eggs, and were generated like the larger ones. Since his time 



* Lewes. 



t Quarterly Journal of Microscopical Science, vol. ii. p. 96. 



