CHAPTER IX 

 THE MECHANISTIC CONCEPTION OF LIFE 



This seems to be the proper place to say something about the 

 " materialistic " — or, as it is now termed, the " mechanistic " — 

 view of the living organism, for, although we have assumed such 

 an hypothesis in all that has been said so far, we are about to 

 abandon it, or, at least, we are about to give to " mechanism " 

 a meaning that is rather different from the one that is usually 

 accepted. Our description of the animal body was first of all 

 mechanical, then we had to make use of physical and chemical 

 ideas, and now we must search for some other concept, which 

 must, nevertheless, still be a logical one. 



The body of the higher animal, then, is a system of muscles 

 and other soft parts which are built up round about, or are 

 supported by a system of rigid parts — the skeleton. The latter 

 consists of separate bones immovably attached together, as in 

 the case of the parts of the skull and pelvis, or movably attached, 

 as in the case of the vertebral column and the skeletons of the 

 limbs. In the former cases the skeleton acts as the supports of 

 the soft organs — thus the skull contains the brain and the great 

 sense organs — while in the latter cases the vertebrae and limbs 

 are the apparatus of movement. 



Where the bones move on each other they are said to be 

 articulated, and the configurations of the articulations (or joints) 

 determine the ways in which the movements occur. Muscles, 

 ending in tendons, are attached to these movable bones, and by 

 their lengthening or shortening the parts are made to extend or 

 bend on each other. Thus the enormous variety of movements 

 that an animal can carry out depend on the shapes and lengths 

 of the bones, the configurations of the joints, and the modes of 

 attachment of the muscles and tendons. 



Further, the muscles are supplied with nutritive matter by a 

 series of conduits — the arteries, capillaries, veins, and lymphatic 

 vessels. At a central point of this vascular system is a propul- 

 sive organ, the heart, which keeps the blood and lymph in 

 motion. The directions in which these fluids move are deter- 



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