322 THE CANADIAN NATURALIST. [Sept. 



me that these are generated in the dead flesh; but if I put similar 

 bodies, while quite fresh, into a jar, and tie some line gauze over 

 the top of the jar, not a maggot makes its appearance, while the 

 dead substances, nevertheless, putrefy just in the same way as 

 before. It is obvious, therefore, that the maggots are not 

 generated by the corruption of the meat ; and that the cause of 

 their formation must be a something which is kept away by gauze. 

 But gauze will not keep away aeriform bodies, or fluids. This 

 something must, therefore, exist in the form of solid particles too 

 big to get through the gauze. Nor is one long left in doubt what 

 these solid particles are; for the blow-flies, attracted by the odour 

 of the meat, swarm round the vessel, and, urged by a powerful 

 but, in this case misleading instinct, lay eggs, out of which 

 maggots are immediately hatched, upon the gauze. The 

 conclusion, therefore, is unavoidable ; the mas-gots are not 

 generated by the meat, but the eggs which give rise to them are 

 brought through the air by the flies. 



These experiments seem almost childishly simple, and one 

 wonders how it was that no one ever thought of them before. 

 Simple as they are, however, they are worthy of the most careful 

 study, for every piece of experimental work since done, in regard 

 to this subject, has been shaped upon the model furnished by the 

 Italian philosopher. As the results of his experiments were the 

 same, however varied the nature of the materials he used, it is not 

 wonderful that there arose in Redi's mind a presumption, that in 

 all such cases of the seeming production of life from dead matter, 

 the real explanation was the introduction of living germs from 

 without into that dead matter — (Redi, Esperienze, pp. 14-16). 

 And thus the hypothesis that living matter always arises by the 

 agency of pre-existing living matter, took definite shape; and had 

 henceforward a right to be considered and a claim to be refuted, 

 in each particular case, before the production of living matter in 

 any other way could be admitted by careful reasoners. It will be 

 necessary for me to refer to this hypothesis so frequently, that, to 

 save circumlocution, I shall call it the hypothesis of Biogenesis ^ 

 and I shall term the contrary doctrine — that living matter may bo 

 produced by not living matter — the hypothesis of Ahiogenebis. 



In the seventeenth century, as I have said, the latter was the 

 dominant view, sanctioned alike by antiquity and by authority ; 

 and it is interesting to observe that Redi did not escape the 

 customary tax upon a discoverer, of having to defend himself 



