28 THOUGHTS ON NATURAL PHILOSOPHY. 
but when you remember that the difference between life and 
death in the seed, and cell, is really the difference between 
the feebleness and swiftness of movements, in various ways, 
of small portions of matter the subject becomes quite easy. 
If they move at sufficient speed, on the addition of the 
needful fluid, life is manifested ; if the speed of movement is 
too feeble it is death, they are inanimate, life is consequently 
at bottom a question of speed. 
The difference between the living and the non-living is 
the capacity possessed, as a result of speed, by the living to 
produce the electro-chemical and other effects within their 
cells that result in growth. Nevertheless the living are not 
independent, they also are dependent on external as well as 
internal physical law, they are electro-chemical machines 
connected with and controlled by the great machine nature; 
and perhaps the best definition of life is that it consists in 
an arrangement of suitable materials, by material motion, in 
suitable form, moving within certain rates of speed. As we 
approach the borderland between animate and inanimate 
nature it is almost as difficult to separate the living from the 
non-living as it is to distinguish between- the animal and 
vegetable; and it is a question whether we ought not to 
extend the definition of life to include much that is now 
regarded as not living, although perhaps much harm may 
not be done if we remember the difficulty of drawing an 
abrupt dividing line between the two Kingdoms. They 
appear to be imperceptibly merged in one another. This is 
nature’s way and may be taken to be one of the indications 
of the unity of nature, and her dependence on natural law. 
You may not like it, you may prefer what looks to you more 
clear and definite; but nature declines to work according to 
our dictation, she has her own inimitable way of gradual 
and imperceptible mutation. 
