284 EVOLUTION IN BIOLOGY. [LECT. 



arise by a process of " equivocal generation " out of 

 not-living matter; and the aphorism so commonly 

 ascribed to him, " omne vivum ex ovo" and which is 

 indeed a fair summary of his reiterated assertions, 

 though incessantly employed against the modern 

 advocates of spontaneous generation, can be honestly 

 so used only by those who have never read a score 

 of pages of the " Exercitationes." Harvey, in fact, 

 believed as implicitly as Aristotle did in the equivocal 

 generation of the lower animals. But, while the 

 course of modern investigation has only brought out 

 into greater prominence the accuracy of Harvey's 

 conception of the nature and mode of development of 

 germs, it has as distinctly tended to disprove the occur- 

 rence of equivocal generation, or abiogenesis, in the 

 present course of nature. In the immense majority 

 of both plants and animals, it is certain that the germ 

 is not merely a body in which life is dormant or 

 potential, but that it is itself simply a detached por- 

 tion of the substance of a pre-existing living body; 

 and the evidence has yet to be adduced which will 

 satisfy any cautious reasoner that "omne vivum ex 

 vivo " is not as well-established a law of the existing 

 course of nature as " omne vivum ex ovo." 



In all instances which have yet been investi- 

 gated, the substance of this germ has a peculiar 

 chemical composition, consisting of at fewest four 

 elementary bodies, viz. carbon, hydrogen, oxygen, 

 and nitrogen, united into the ill-defined compound 

 known as protein, and associated with much water, 

 and very generally, if not always, with sulphur and 



