242 BIOGENESIS AND ABIOGENESIS vm 



I cannot now discuss, but which looked promising 

 enough in the lights of their time, Buffon and 

 Needham doubted the applicability of Redi's 

 hypothesis to the infusorial animalcules, and 

 Needham very properly endeavoured to put the 

 question to an experimental test. He said to 

 himself, If these infusorial animalcules come from 

 germs, their germs must exist either in the sub- 

 stance infused, or in the water with which the 

 infusion is made, or in the superjacent air. Now 

 the vitality of all germs is destroyed by heat. 

 Therefore, if I boil the infusion, cork it up care- 

 fully, cementing the cork over with mastic, and 

 then heat the whole vessel by heaping hot ashes 

 over it, I must needs kill whatever germs are 

 present. Consequently, if Redi's hypothesis hold 

 good, when the infusion is taken away and allowed 

 to cool, no animalcules ought to be developed in 

 it ; whereas, if the animalcules are not dependent 

 on pre-existing germs, but are generated from the 

 infused substance, they ought, by and by, to make 

 their appearance. Needham found that, under 

 the circumstances in which he made his experi- 

 ments, animalcules always did arise in the 

 infusions, when a sufficient time had elapsed to 

 allow for their development. 



In much of his work Needham was associated 

 with Buffon, and the results of their experiments 

 fitted in admirably with the great French natural- 

 ist's hypothesis of " organic molecules," according 



