92 SCIENCE IN THE LAST HALF CENTURY. 



The popular belief in abiogenesis, or the so-called "spontaneous"^ 

 generation of the lower forms of life, which was accepted by all the 

 philosophers of antiquity, held its ground down to the middle of the 

 seventeenth century. Notwithstanding the frequent citation of the 

 phrase, wrongfully attributed to Harvey, " Omne vivum ex ovo," that 

 great physiologist believed in spontaneous generation as firmly as Aris- 

 totle did. And it was only in the latter part of the seventeenth century 

 that Kedi, by simple and well-devised experiments, demonstrated that 

 in a great number of cases of supposed spontaneous generation, the 

 animals which made their appearance owed their origin to the ordinary 

 process of reproduction, and thus shook the ancient doctrine to its foun- 

 dations. In the middle of the eighteenth century it was revived in a. 

 new form, by Needham and Buifon ; but the experiments of Spalianzan! 

 enforced the conclusions of Kedi, and compelled the advocates of the 

 occurrence of spontaneous generation to seek evidence for their hypoth- 

 esis only among the jjarasites and the lowest and minutest organisms. 

 It is just fifty years since Schwann and others proved that even with 

 respect to them, the supposed evidence of abiogeuesis was untrust- 

 worthy. 



During the present epoch the question whether living matter can be 

 pi^oduced in any other way than by the physiological activity of other liv- 

 ing n)atter has been discussed afresh withgreatvigorj and the problem has 

 been investigated by experimental methods of a precision and refinemeut 

 uidvuown to previous investigators. The result is that the evidence in 

 fav^or of abiogeuesis has utterly broken down in every case which has 

 been properly tested. So far as the lowest and minutest organisms are 

 concerned, it has been j)roved that they never make their appearance 

 if those i)recautions by which their germs are certainly excluded are 

 taken. And, in regard to parasites, every case which seemed to make 

 for their generation from the substance of the animal or plant which 

 they infest has been proved to have a totally diiferent significance. 

 Whether not-living matter may pass, or ever has under any conditions 

 passed into living matter, without the agency of pre-existing living 

 matter, necessarily remains an open question; all that can be said is 

 that it does not undergo this metamorphosis under any known condi- 

 tions. Those who take a monistic view of the physical world maj^ fairly 

 hold abiogeuesis as a ijious opinion, supported by analogy and defended 

 by our ignorance. But, as matters stand, it is equally justifiable to re- 

 gard the physical world as a sort of dual monarchy. The kingdoms of 

 living matter and of not-living matter are under one system of laws, 

 and there is a perfect freedom of exchange and transit from one to the 

 other. But no claim to biological natiouality is A'aiid except birth. 



In the department of anatomy and development a host of accurate 

 and patient inquirers, aided by novel methods of preparation, which 

 enable the anatomist to exhaust the details of visible structure and to 

 reproduce them with geometrical precision, have investigated every 



