110 
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. Erom 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 substances 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 state- 
ment was generally believed. 
In 1829 the author’s late father repeated many of Dr. Brown’s 
experiments, and, to prove that these moving particles 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 showed 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, indeed, modern 
ones, should have mistaken them for animalculae. The particles 
which exhibit the greatest activity are exceedingly minute, rang- 
ing from 10,000th to 30,000th of au inch in diameter ; they 
remain active a considerable time if they are nearly of the same 
specific gravity as the solution in which they are immersed. One 
simple mode of producing them is to rub a little gamboge in 
water, on a glass slide, and place a thin glass cover on it, using a 
power of from 800 to 1200 diameters. They can easily be dis- 
tinguished with less magnifying power, but are not so effectually 
shown. If they are required for prolonged examination, Dr. 
Brown recommends that the solution of gamboge be mixed with 
a little almond oil. The minute globules of water are thus sur- 
rounded by oil, and rapid evaporation is prevented. 
The cause of the phenomenon is not yet satisfactorily accounted 
for. Some have imagined that it is the physical repulsion of the 
particles when uninfluenced by gravitation. The author has 
tried many experiments with electricity and magnetism without 
success. He thinks that the movement may possibly be con- 
nected with the absorption and radiation of heat. 
Those interested in Dr. Brown’s experiments and observations 
on active molecules can refer to his republished papers in vol. i, 
of the Bay Society’s publications for 1866. 
