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itself as vital force will depend on the property being sustained by suitable 
influences from without. Thus we must accept vitality as an ultimate fact, 
real and patent to every intelligence, until we choose to give it another 
name, which we may imagine that we understand better. Vitality is 
conceivable as a property of matter having a given composition ; but vital 
force, in-so-far as it depends on the continuance of external agencies of a 
material character, and expresses the reaction of "living matter," must be 
a product of physical or chemical change. Organic matter offers the 
conditions necessary to the evolution of animal life, but ' ' vital force " can 
only be understood at present in this sense— that it is set free by the play 
of material affinities, and in its turn influences the future behaviour 
of the organism, as its elements grow more and more composite. 
To affirm that an animal Jives only by virtue of some intrinsic dominant 
power seems to me to be stating but one half of the case, as it presents no 
explanation of the tenure of that life. The mere existence of an animal 
implies the presence, and depends on the nature and determining influence 
of external media. This is the basis of its power to live. Where life 
persists through varying conditions, it may be said that this is due to 
tenacity of vital power, but it may with more truth be said that a certain 
variety of conditions is compatible with the preservation of organic matter 
in such state, that its so-called inherent vital properties are not destroyed. 
The capacity of adaptation to cosmic influences is, on the whole, limited ; 
but within those limits what is called tenacity of life, instead of being 
interpreted as an effort of vital force, may be better understood as the 
compatibility of organic matter to exist without injury by accepting 
passively the conditions imposed in it. But the life thus continued under 
different circumstances becomes changed by them, and we have variety 
of life under variety of conditions through the instrumentality of the 
remoulded organic matter. The persistence of external conditions and 
internal adaptation affords us a rationale of the persistent types of 
animals. And "variation of conditions" gives us the explanation 
of variation in type. But in all this we see little of controlling 
power, in the sense of "vital force" ; the animal cannot resist external 
influences, but is moulded by them or dies. Thus, for instance, 
our Fresh- Water Amoeba dies in sea-water, or a solution of 1^ per 
cent. salt. In more diluted solutions it lives for a time, and change of 
form and movement indicate the effect of the new medium. 
Allow me for a moment longer to dwell on this point. It is not the number, 
size, or minuteness of created beings that so deeply challenges the attention 
