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the same infusion, and the whole covered with a large bell 
glass, it will be found in eight days that on the surface of the 
former are numerous ciliated animalcules, while on that of the 
latter only bacteria and vibrios exist. The experiment may be 
reversed, for if the shallow vessel be filled to the brim, and 
the deep vessel lias only its bottom covered, then the ciliated 
microzoa will appear in the former, and the non-ciliated in the 
latter.” What does this prove beyond the well-known truth 
that certain creatures will be developed in shallow water, and 
others only in deep water ? The salmon seeks the bed of the 
shallow stream, on which to spawn, while other fishes seek 
deeper bottoms, because their ova are hatched best in different 
situations. What has this to do with the origin of life in matter 
whose organized character has been destroyed ? It shows 
only the well-known truth that in varied conditions forms of 
life are variously brought forth — that the seed of a fir-tree will 
grow where that of a palm will lie dormant. 
13. Professor Bennett says that “the conclusion which we 
must arrive at, therefore, is that the molecules seen on the 
surface of infusions out of which animalcules and fungi are 
produced, are not derived from the air.” Here I can so far 
agree with him. But he says: — “Neither can they be 
supposed to pre-exist in the fluid, as then they would be 
readily seen, which they never are at the commencement. On 
this point nothing can be clearer than the microscopical evi- 
dence.” * What are Dr. Bennett's own words in another com- 
munication of his on this very point ? He says, “ The ultimate 
molecule has never been reached, even with the highest magni- 
fying powers. In the same manner that the astronomer with his 
telescope resolves nebulae into clusters of stars, and sees other 
nebulae beyond them, so the histologist, with his microscope, 
magnifies molecules into gemmules, and sees further molecules 
come into view.”f Here, then, is a portion of the film which 
is taken from the surface of the infusion, and placed under the 
microscope. It is magnified into molecules. One of these is 
seen to unite with another, and two unite with a third, these 
with a fourth, and so on. But “ the first change visible to the 
eye,” he says, is a slight “ opalescence.” Let us note this 
slight “ opalescence .” { Previous to this change nothing is 
seen in the infusion, but soon after this change has taken 
place, under high magnifying powers molecules may be seen. 
What, then, is the nature of the clear evidence that these 
* The Atmospheric Germ Theory, p. 17. 
t Paper “ On the Molecular Theory of Generation,” from the Proceedings 
of the Royal Society of Edinburgh, p. 2. 
X The Atmospheric Germ Theory, p. 8. 
