6 LIVERPOOL BIOLOGICAL SOCIETY. 
an effort of the fundamental power of the planetary 
system to produce a change of seasons on the planets, or 
to say that the ebb and flood of the tides are the reaction 
of the organism of the earth upon the moon. When 
speaking of a physical explanation of organic phenomena, 
it is not necessary to understand an explanation by 
known physical powers, such, for example, as_ that 
universal refuge electricity, and the hike; but an explana- 
tion by means of powers which operate lke the physical 
powers in accordance with strict laws of blind necessity 
whether they be also to be found in inorganic nature or 
not. As the elementary materials of organic matter are 
not different from those of the inorganic kingdom, the 
source of the organic phenomena can only reside in 
another combination of these materials.’’* 
The same opinions, supported by very similar arguments, 
had already been expressed in Fletcher’s ‘‘ Physiology,”’ 
three years before Schwann’s work appeared. The above 
agrees marvellously with the protoplasmic theory of life, 
the main proposition of which is that an altered com- 
bination of the elements is all sufficient to produce the 
property of vitality; and that the recognition of this 
pecuhar state of combination may be accepted as an 
explanation, or at any rate the groundwork for a defini- 
tion, whether we can understand its nature, or reproduce 
it in the laboratory, or act upon it at all therein except by 
destruction. The recognition of the law of gravitation 
has been of incalculable service in physical science, 
although the physical cause of gravity remains as yet 
undiscovered. We are now prepared to enter on a 
criticism of the definitions of life. 
The majority of the earlier followers of John Brown, in 
discarding the vital principle hypothesis, simply define life 
* Cell Theory, p. 186. 
