SPONTANEOUS GKNERATlON. 587 
were realized, so that the germ theory fulfills 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 
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 Eoberts, " 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. 
