(IKNEtlATlON. 



were realized, so that the germ theory fulfills the test of 

 every true theory, that test being the power of prevision. 



When "nuked or almost naked specks of protoplasm" 

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

 objective truth of Nature. Such words sound like the 

 words of knowledge where knowledge is really nil. The 

 possibility 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 un- 

 covered pea to pulp. The pellicle prevents imbibition, 

 diffusion, and the consequent disintegration. A greasy or 

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

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

 singular resistance of green vegetables to sterilization," 

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

 peculiarity of the surface, perhaps their smooth glistening 

 epidermis which prevented complete wetting of their sur- 

 faces." I pointed out in 1876 that the process by which an 

 atmospheric germ is wetted would be an interesting sub- 

 ject of investigation. A dry microscope covering-glass may 

 be caused to float on water for a year. A sewing-needle 

 may be similarly kept floating, though its specific gravity 

 is nearly eight times that of water. Were it not for some 

 specific relation between the matter of the gerrn and that 

 of the liquid into which it falls, wetting would be simply 

 impossible. Antecedent to all development there must be 

 an interchange of matter between the germ and its environ- 

 ment; and this interchange must obviously depend upon 

 the relation of the germ to its encompassing liquid. Any- 

 thing that hinders this interchange retards the destruction 

 of the germ in boiling water. In my paper published in 

 the "Philosophical Transactions" for 1877, I add the 

 following remark: 



It is not difficult to see that the surface of a seed or germ may be 

 so affected by desiccation and other causes as practically to prevent 

 contact between it and the surrounding liquid. The body of a germ, 

 moreover, may be so indurated by time and dryness as to resist 

 powerfully the insinuation of water between its constituent mole- 

 cules. It would be difficult to cause such a germ to imbibe the 

 moisture necessary to produce the swelling and softening which 

 precede its destruction in a liquid of high temperature. 



