116 THE PROGRESS OF SCIENCE n 



the ordinary process of reproduction, and thus 

 shook the ancient doctrine to its foundations. In 

 the middle of the eighteenth century, it was 

 revived, in a new form, by Needham and Buffon ; 

 but the experiments of Spallanzani enforced the 

 conclusions of Redi, and compelled the advocates 

 of the occurrence of spontaneous generation to seek 

 evidence for their hypothesis only among the 

 parasites 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 abiogenesis was untrust- 

 worthy. 



During the present epoch, the question, whether 

 living matter can be produced in any other way 

 than by the physiological activity of other living 

 matter, has been discussed afresh with great 

 vigour ; and the problem has been investigated by 

 experimental methods of a precision and refine- 

 ment unknown to previous investigators. The 

 result is that the evidence in favour of abiogenesis 

 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 

 proved that they never make their appearance, if 

 those precautions by which then* germs are 

 certainly excluded are taken. And, in regard to 

 parasites, every case which seemed to make t'< >r 

 their generation from the substance of the animal, 

 or plant, wliioli they infest has been prove 1 to 



