51 
ON THE MOLECULAK OKIOIN OF INFUSOEIA. 
By JOHN HUGHES BENNETT, M.D., F.B.S.E., 
Professor of the Ihstituxes of Medicine in the University of 
Edinburgh, &c., &c. 
REVIOUS to the time of W. Harvey, life was considered to 
be an independent principle capable of being added to, 
or removed from, inert matter. Such was the opinion of the 
ancient philosophers as allegorically explained by the fable of 
Prometheus, who animated the marble statue by fire stolen 
from heaven. But our modern view of life is, not that it is 
independent of matter but a condition of matter; in other 
words, that material substances, found in the atmosphere and in 
plants and animals, influenced by certain forces, have peculiar 
properties communicated to them. These properties are con- 
tractility, sensibility, the power of growth in certain directions 
and mental acts — the existence and exercise of any one of 
which constitute life. 
Harvey put forth the law omne vivum ex ovo ; and since his 
day the belief has been general, that animals and plants are de- 
rived from eggs or seeds ; that vitality is always transmitted, 
and never created ; and that, where these fundamental principles 
cannot be recognised, the minuteness of the germs and their 
wide diffusion throughout nature, and more especially in the 
atmosphere, offer a sufficient explanation of what may appear 
mysterious. Nature, it was argued, must be uniform in her 
operations, and analogy warrants our supposing that the same 
law of generation, which applies to the higher animals and 
plants, is equally applicable to the lower. 
In later times, Buffon imagined life, like matter, to be in- 
destructible. According to him every living molecule had a 
life of its own, and the method by which it manifested its func- 
tion depended on its association with other molecules. Thus, 
the body of an animal or a plant was the aggregation of a 
multitude of minute living beings arranged in a particular 
way. The death of the complex compound was simply a disso- 
lution of one of these associations, and the organic molecules 
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