iv MECHANISM AND TELEOLOGY 303 



of these constituents to one another. Mechanically, the 

 organism may be conceived, like any other machine, as 

 essentially an arrangement for the transformation of energy. 

 Thus the animal organism takes up energy in the form of 

 food on the one hand and of oxygen on the other. For 

 each process of absorption it has its appropriate mechanism, 

 the alimentary and the respiratory organs. Next, it has to 

 distribute what it absorbs by means of its circulatory 

 system, and thereby to nourish nerve and muscle tissues 

 wherein the potential energy of the foodstuffs is converted 

 into energy of motion, so directed through the nervous 

 control as to secure fresh supplies of energy and at the same 

 time maintain at the right point, neither too high nor too 

 low, the temperature at which this persistent activity of 

 change or metabolism can go on. Finally, the waste pro- 

 ducts which result have to be eliminated, for which purpose 

 the circulatory, respiratory and alimentary systems, together 

 with other special organs as the kidneys, again come into 

 play. Of the reproductive functions we need not here 

 take account. It is enough to recall in rough-and-ready 

 way the picture familiar to common sense and elaborated 

 in detail by physiology of the individual organism as a 

 going concern in which a total process, the metabolism or 

 life of the organism, is maintained by the co-operation of a 

 series of parts, the final result of which, when it comes full 

 circle, is just self-maintenance. 



Now, at any rate, as long as we ask no questions about 

 origins there is nothing here to differentiate the organism 

 from the well-compacted machine. In fact, the physio- 

 logist in seeking explanations of the life process moves 

 habitually, and often with brilliant success, along the lines 

 of mechanical explanation. Thus he can follow the circu- 

 lation of the blood by conceiving the heart as a force pump 

 and the arteries and veins as a connected system of elastic 

 tubes. He may begin with the left ventricle, and show 

 how the blood is expelled by a strong contraction which, 

 closing the valves that lead back into the auricle, open those 

 of the aorta. He will show that this new tide of blood, 

 aided, moreover, by the contraction of the aorta itself, will 

 propagate a pulse through the arterial system and force the 



