730 HANDBOOK OF PHYSIOLOGY. 



eration, which consists in the natural production and separation of a 

 portion of organized structure, with power itself to transform force so as 

 therewith to build up an organism like the being from which it was 

 thrown off, is another distinctive peculiarity of a living being. We 

 know of nothing like it in the organic world. And the distinction is 

 the greater because it is the fulfilment of a purpose, towards which life 

 is evidently, from its very beginning, constantly tending. It is as 

 natural a destiny to separate parts which shall form independent beings 

 as it is to develop a limb. Hence it is another instance of that carrying 

 out of certain projects, from the very beginning in view, which is so 

 characteristic of things living and of no other. 



It is especially in the discharge of what are called the animal func- 

 tions that we see vital force most strangely manifested. It is true that 

 one of the actions included in this term namely mechanical movement 

 although one of the most striking, is by no means a distinctive one. 

 For it must be remembered that one of the commonest transformations 

 of physical force with which we are acquainted is that of heat into me- 

 chanical motion, and that this may be effected by an apparatus having 

 itself nothing whatever to do with life. The peculiarity of the mani- 

 festation in an animal or vegetable is that of the organ by which it is 

 effected, and the manner in which the transformation takes place, not 

 in the ultimate result. The mere fact of an animal's possessing capa- 

 bility of movement is not more wonderful than the possession of a simi- 

 lar property by a steam engine. In both cases alike, the motion is the 

 correlative expression of force latent in the food and fuel respectively; 

 but in one case we can trace the transformation in the arrangement of 

 parts, in the other we cannot. 



The consideration of the products of the transformation of force 

 effected by the nervous system would lead far beyond the limits of the 

 present chapter. But although the relation of mind to matter is so 

 little known that it is impossible to speak with any freedom concerning 

 such correlative expressions of physical force as thought and nerve-pro- 

 ducts, still it cannot be doubted that they are as much the results of 

 transformation of force as the mechanical motion caused by the con- 

 traction of a muscle. But here the mystery reaches its climax. We 

 neither know how the change is effected, nor the nature of the product, 

 nor its analogies with other forces. It is therefore better, for the pres- 

 ent, to confess our ignorance, than, with the knowledge which we have 

 lately gained to build up rash theories, serving only to cause that con- 

 fusion which is worse than error. 



It may be said, with perfect justice, that even if the foregoing con- 

 clusions be accepted, namely, that all manifestations of force by living 

 beings are correlative expressions of ordinary physical force, still the 

 argument is based on the assumption of the existence of the apparatus 



