SPONTANEOUS GENERATION 339 



put aside for ten or twelve hours, and the process of heat- 

 ing is repeated. We thus kill the germs in the order of 

 their resistance, and finally kill the last of them. No infu- 

 sion can withstand this process if it be repeated a suffi- 

 cient number of times. Artichoke, cucumber, and turnip 

 infusions, which had proved specially obstinate when in- 

 fected with the germs of desiccated hay, were completely 

 broken down by this method of discontinuous heating, 

 three minutes being found sufficient to accomplish what 

 three hundred minutes' continuous boiling failed to ac- 

 complish. I applied the method, moreover, to infusions 

 of various kinds of hay, including those most tenacious of 

 life. Not one of them bore the ordeal. These results 

 were clearly foreseen before they were realized, so that 

 the germ theory fulfils the test of every true theory, that 

 test being the power of prevision. 



When "naked or almost naked specks of protoplasm" 

 are spoken of, the imagination is drawn upon, not the ob- 

 jective truth of Nature. Such words sound like the words 

 of knowledge where knowledge is really nil. The possi- 

 bility of a "thin covering" is conceded by those who 

 speak in this way. Such a covering may, however, exer- 

 cise a powerful protective influence. A thin pellicle of 

 India-rubber, for example, surrounding a pea keeps it 

 hard in boiling water for a time sufficient to reduce an 

 uncovered pea to a pulp. The pellicle prevents imbibition, 

 diffusion, and the consequent disintegration. A greasy or 

 oily surface, or even the layer of air which clings to cer- 

 tain bodies, would act to some extent in a similar way. 

 "The singular resistance of green vegetables to steriliza- 

 tion," says Dr. William Roberts, "appears to be due to 

 some peculiarity of the surface, perhaps their smooth 



