4 THE THEORY OF SPONTANEOUS GENERATION. 



rous fluctuations, about the middle of the present century. From 

 among the numerous investigators who took part in this contro- 

 versy, mention can here be made of but few Needham on the one 

 side and Spallanzani on the other being entitled to the first place. 



3. Needham's Demonstration in Favour of 

 ".Generatio ^quivoea." 



The most energetic champion of the theory of spontaneous 

 generation was the English divine, NEEDHAM (I.). This theory 

 was in existence long before his time, and had had renowned 

 supporters among them the chemist Yan Helmont, who pro- 

 posed a method for producing artificial mice but until then had 

 not progressed beyond the stage of indefinite assertion and un- 

 founded hypotheses. The cause of the extraordinary support and 

 approval accorded to the assumptions put forward by the English 

 divine is, on the other hand, attributable to the novel manner in 

 which he arrived at his theory (published in 1745), viz., not by 

 untenable hypotheses, but by well-directed experiments. 



He set to work, for example, in the following manner : An 

 aqueous meat extract was boiled for a short time in a flask, which 

 was then made air-tight and left to stand for several days or 

 weeks. When opened at the end of this time, the contents 

 proved to be plentifully infested with ''infusoria," from which 

 Needham concluded that as the " eggs " originally present in the 

 liquid were killed by the boiling and the entry of fresh ones 

 from the outside was precluded, therefore the living infusoria 

 discovered in the liquid on re-opening the flask must have origi- 

 nated spontaneously, not from eggs (germs), but from the lifeless 

 constituents of the liquid. 



The great impression produced on his contemporaries by these 

 statements can be appreciated by reference, for instance, to 

 Buffon's work on the " System of Generation." 



4. Spallanzani's Experiments. 



Of the two hypotheses forming the basis of Needham's 

 deduction, the accuracy of the second, i.e. that relating to the 

 exclusion of outside germs, was examined first. Some twenty 

 years after the appearance of the English theory, the Abb6 

 SPALLANZANI (I.) published a dissertation in which he combated 

 the doctrine of spontaneous generation. In this work the Italian 

 divine detailed the experiments which had led him to the con- 

 clusion that a development of the animalculse in question, in an 

 infusion maintained at boiling-point for three-quarters of an hour, 

 was only possible provided air, which had not been previously 

 exposed to the influence of fire, had been admitted. This position 

 was also maintained by Spallanzani in a second treatise (II.). 



