18 Correlation of Mieroscojpic Physiology [*jTu?nL,SrMS' 
There are probably some grounds for believing tbat the particles 
or molecules in magnets are always in motion. Mr. Wenham once 
told me that he had seen a cavity in a crystal partially filled with 
a fluid, and for several years this fluid had been unceasingly in 
motion, although completely shut off from the surrounding atmo- 
sphere. 
Motion, then, is not pecuHar to life, and we shall be brought at 
last to the single distinction — reproduction. 
The difficulty here would be insuperable if we were compelled 
to accept the hypothesis that life is transmitted from one organism 
to another. But this hypothesis is no longer generally accepted. 
Prof. Owen, who has been until recently opposed to such views, has 
at length accepted the hypothesis of spontaneous generation. 
An article in * Scientific Opinion,' April 28, thus tersely states 
the case in favour of this hypothesis: — "If when we expose an 
organic infusion to the air it soon becomes peopled by myriads of 
animal and vegetable forms, either these have been formed sponta- 
neously, or their ova have been carried to the infusion through the 
atmosphere. Now the latter alternative involves an hypothesis 
difficult to prove, and as yet far enough from demonstration. It 
insists on the supposition that the air is charged with the germs of 
the animals and plants. But is this the case ? There seems to be 
but very little testimony in its favour. M. Pasteur asserts that 
it is so. But Bennett, Pouchet, and several others skilled in the 
use of the microscope, have failed absolutely to detect these ubi- 
quitous germs. Whence, then, are they derived, if not from the 
decomposing organic matter ? Many of those who are still sceptical 
as to heterogeny, admit that they have watched the conversion of 
bacteria into fungoid growths ; and some have even alleged that they 
have witnessed the conversion of bacteria into infusoria. Surely 
these are as difficult statements to digest as the theory of sponta- 
neous generation." 
Chemists were wont until very recently to divide all substances 
into organic and inorganic. Even then an account had to be given 
of the compounds in salts formed by the union of metals with 
organic acids. Now in the latest works we find a list of substances 
called organo-metallic bodies, in which the metals zinc, tin, cad- 
mium, mercury, magnesium, aluminium, and glucinum are directly 
combined with organic radicles. In these compounds zinc may be 
found as a constituent of a volatile ether. 
There is no boundary line then between organic and inorganic 
substances, neither is there any boundary line between plants and 
animals, Diatomaceae being placed by some observers in the animal, 
and by others in the vegetable kingdom. Eeasoning by analogy, 
I believe that we shall before long find it an equally difficult task 
to draw a distinction between the lowest forms of living matter and 
