Page:The Harveian oration - delivered at the Royal College of Physicians, London, June 24, 1870 (IA b22307643).pdf/20

18 ception we form of germs and ova is as faulty as was that of early physiologists respecting the generation of elementary substances by organic bodies, or of that till lately generally entertained, and still entertained by some, respecting the vital forces, as if they were not terrestrial. That living things throw off at times portions of their mass, which become through a definite set of physical relations like the parent from which they sprang, is of common experience; but whether these masses, germs or ova as they may happen to be called, are as limited and specific as we have hitherto regarded them, is the questio vexata of the day.

That like should beget like, might à priori be inferred from the equality of the conditions. But observation also shows that, the conditions varying, like does not necessarily beget likeness; and this variation occurs both upwards towards a higher organization, downwards towards an extinction of it, and divergently towards variety of organic form.