Rev. P. Keith 07i the Conditions of Life. 35 



as may be seen by perusing his Sylva Sylvarum. The mosses 

 that grow on trees he regards as being nothing more than a 

 sort of excretion which the tree cannot assimilate; and the 

 misletoe he represents as being produced, not from seed, but 

 merely from superabundance of nourishment. 



Yet the truth of the doctrine began to be at last suspected, 

 and subjected to the test of observation and experiment. It 

 was a scrutiny which it could not stand, and beneath which it 

 fell refuted. The credit of the refutation is due partly to 

 Harvey, who contended that all animals spring from an egg 

 deposited bj' a parent, — omne animal ex ovo ; and partly to 

 Francisco Redi, an Italian philosopher and physician, whose 

 experiments are well known, together with their result; 

 namely, that there is no such thing as a generation of insects 

 from putrefaction. Similar investigations were applied to the 

 vegetable kingdom by Malpighi and others, with similar re- 

 sults, demonstrating that all plants spring from seed, the pro- 

 duce of a parent, — omnis jilanta e semine. In short the doctrine 

 of equivocal generation came into universal disrepute; and 

 the stories of showers of frogs that fell from the clouds, and 

 of armies of insects engendered by the east wind, and wafted 

 on its wings, together with the marvellous account of a plane 

 tree that sprang up spontaneously out of a brazen tripod, as 

 related by Theophrastus, were no longer credited. 



Such was the triumph of truth over error. Yet the very 

 progress of the science that achieved it gave rise to new 

 doubts. In the advance of microscopical discovery, a new 

 world was laid open to the view of man, namely, that of the 

 animalcula infusoria and spermatica. The most successful of 

 the earlier operators in this department were Leuwenhoeck, 

 Needham, and Swammerdam. Leuwenhoeck estimated the size 

 of the smallest of these minute animalcules, and found that 

 upwards of 1,000,000 of them might be contained in a space 

 not larger than that occupied by a grain of coarse sand * . 

 Concerning their origin every philosopher had his own opinion. 

 Some regarded them as being generated by parents of the 

 species, rather from analogy, than from any direct proof, which, 

 in objects so minute, it nuist be next to impossible to obtain. 

 Buffbn regarded them as being, not the product of generation, 

 not germs or embryos, not either animals or vegetables, but 

 merely organic and moving particles proper to compose a 

 living being. — If this were really the case, the species or vari- 

 eties of animalcula would be interminable, as there would be 

 no end to new combinations ol" orgiinic particles, and no cer- 

 tainty ol' finding tomorrow the species you may have met 



' I'liil. Tians. Abridf^cri ; vol. ii. .377. and vol. iii. 20.'*. 



Y '1 willi 



