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the examination of the pollen of other plants, the particles 
of which he found to exhibit similar activity. For some 
time he was exceedingly perplexed with these phenomena, 
and was disposed to believe that he had really seen in these 
minute bodies the supposed constituents or elementary 
molecules of organic bodies, first so considered by Buffon, 
Wrisberg, Muller, and Milne Edwards, and on examining 
various animal and vegetable tissues, whether living or 
dead, he found, as he had expected, that active molecules 
were visible by merely bruising the substances in water. 
Continuing his observations, he found that particles from 
a bruised specimen of fossil wood appeared to consist 
entirely of these moving bodies. From this he inferred 
that these molecules were not limited to organic bodies, or 
even to their products. 
After this he proceeded to examine minerals, simple 
earths, metals, and many other substance too numerous to 
mention, and with similar results. 
Some writers who commented on these experiments, but 
who had not carefully followed his communications, asserted 
that Dr. Brown imagined these particles to be animated, — 
and this statement was generally believed. 
In 1829 the author’s late father repeated many of Dr. 
Brown’s experiments, and to prove that these moving par- 
ticles could not be animalculse, he placed some crystals and 
minerals in a crucible which he subjected to a red heat, 
ground portions of them to powder, then put it into 
distilled water, and shewed the particles in motion to his 
scientific friends. It is now well known that all kinds of 
matter, if reduced to sufficiently small particles, and placed 
in a medium in which they will not readily sink, will 
exhibit these movements. 
Now, as this phenomenon occurs in the cells of plants, the 
yolk of the egg, and in decomposing animal and vegetable 
matter, it is not surprising that the early microscopists, and, 
