340 THE BEGINNINGS OF LIFE. 



was quite inclined to believe for a time, on the strength 

 of his own experiments, that Schwann's precautions, 

 properly carried out, were adequate to prevent the 

 occurrence of organisms in the experimental fluids. 

 These early investigations were made with sweetened 

 yeast- water, concerning which M. Pasteur says *, c I 

 have certainly had occasion to repeat the experiment 

 more than fifty times, and in no case has this fluid, 

 otherwise so changeable, shown a vestige of organism 

 when in the presence of calcined air.' But after a 

 time M. Pasteur began to employ an entirely different 

 fluid, and in all these experiments living organisms 

 were invariably present in the previously boiled fluids 

 from recently opened flasks. Formerly he used c 1'eau 

 de levure sucree,' but now he employed milk a complex 

 and highly nutritive fluid. There was no necessary 

 contradiction in these results. Facts which had been 

 thoroughly established with regard to the one fluid 

 might not necessarily hold good for the other. A 

 consideration so obvious as this ought to have -keen 

 entertained by any unbiassed experimenter, but it was 

 not even hinted at by M. Pasteur. As on other occa- 

 sions, when his experiments admitted of two interpre- 

 tations, M. Pasteur spoke only of one. He completely 

 ignored an equally possible interpretation 7 the very 

 existence of which he left his readers to ascertain for 

 themselves. Thus, speaking of his experiments with 

 boiled milk and calcined air in closed vessels, he 



1 Loc. cit., p. 36, note (i). 





