20 THOUGHTS ON NATURAL PHILOSOPHY. 
Some may ask: If that be so, why is it that material 
motion does not now originate life on the earth? It is not 
absolutely certain that it does not; but if it no longer dces 
so, the reply is, that circumstances are not now favourable ; 
the earth has cooled, the material movements of its particles, 
atoms, etc., are slower. At one time, when it was hotter, 
and the movements were more rapid, this earth must have 
been a vast hot-bed for the production of vegetable and 
animal life. 
“One fundamental fact in plant physiology practically 
contradicts the assumption that life has never originated 
from inorganic substances ; namely, at the present time living 
substance is being continually formed in the plant cell from 
simple inorganic compounds, carbonic acid, water, sulphates, 
nitrates, etc. Between the small seed put into the earth in 
the spring and the huge plant that grows from it during the 
summer, an enormous quantity of living substance has been 
formed out of the purely inorganic substances of the environ- 
ment, and when winter comes, almost the whole quantity of 
this living substance returns again to simpler inorganic 
compounds. It is here seen how inseparably related are 
inorganic and organic nature, how living substance is 
originating continually from lifeless substance, and is 
continually being decomposed again into lifeless substance. 
Nageli (’84) one of the most talented botanists, says rightly: 
—‘ One fact—that in organisms inorganic substance becomes 
organic substance, and that the organic returns completely to 
the inorganic—is sufficient to enable us to deduce by means 
of the law of causation the spontaneous origin of organic 
nature from inorganic.’ If in the physical world all things 
stand in casual connection with one another, if all phenomena 
proceed along natural paths, then organisms, which build 
themselves up from and finally disintegrate into the sub- 
