SPONTANEOUS GENERATION 309 



fectlj visible to an eye strengthened by the microscope. 

 With reference to their origin these organisms were called 

 "Infusoria." Stagnant pools were found full of them, and 

 the obvious difficulty of assigning a germinal origin to ex- 

 istences so minute furnished the precise condition neces- 

 sary to give new play to the notion of heterogenesis or 

 spontaneous generation. 



The scientific world was soon divided into two hostile 

 camps, the leaders of which only can here be briefly al- 

 luded to. On the one side, we have Birffon and Need- 

 ham, the former postulating his " organic molecules," and 

 the latter assuming the existence of a special "vegetative 

 force" which drew the molecules together so as to form 

 living things. On the other side, we have the celebrated 

 Abbe* Lazzaro Spallanzani, who in 1777 published results 

 counter to those announced by Needham in 1748, and ob- 

 tained by methods so precise as to completely overthrow 

 the convictions based upon the labors of his predecessor. 

 Charging his flasks with organic infusions, he sealed their 

 necks with the blowpipe, subjected them in this condition 

 to the heat of boiling water, and subsequently exposed 

 them to temperatures favorable to the development of life. 

 The infusions continued unchanged for months, and when 

 the flasks were subsequently opened no trace of life was 

 found. 



Here I may forestall matters so far as to say that the 

 success of Spallanzani 's experiments depended wholly on 

 the locality in which he worked. The air around him 

 must have been free from the more obdurate infusorial 

 germs, for otherwise the process he followed would, as 

 was long afterward proved by Wyman, have infallibly 

 yielded life. But his refutation of the doctrine of spon 



