68 THE NATURE AND ORIGIN OF LIFE 



cranks and so on ; and it would seem difficult for two 

 engineers, each having to describe the locomotive's working, 

 to decompose it in two different ways. Besides, the loco- 

 motive is an instrument conceived by man and executed 

 by him with a view to a certain function. 



On the contrary, when we have to decompose the total 

 activity of a living being into partial and simpler functions, 

 we should think there might be very many different ways 

 of doing it and so there are. But physiologists for the 

 most part agree in using the same method and have thus 

 created a language of analysis adopted by all. 



To tell the truth, in an animal like man we find certain 

 elements of action always comparable among themselves 

 in the execution of a great number of different acts ; they 

 are like so many wheels in an industrial machine. Such, 

 for example, are rigid bone segments, articulations, muscles, 

 tendons, veins and arteries, nerves and the rest. Whenever 

 a man's body executes a movement, we can decompose the 

 movement into several parts corresponding to each of these 

 elements of action. In such a case anatomy guides the 

 physiological description of the phenomenon observed. 



For the analysis of a locomotor act such decomposition 

 is not only useful, it is indispensable. Yet it has many 

 drawbacks. It leads the analyst to consider the different 

 segments of the apparatus he is studying as independent 

 of each other except in their relations with the mechanism, 

 just as connecting-rods and cranks and wheels in the loco- 

 motive, each of which exists by itself, are independent of 

 each other except in their relations with the mechanism. 

 Now bones, muscles, nerves, are the living elements of 

 one and the same organism and share in conditions of 

 existence common to all. When a muscle contracts, it 

 draws together two bone segments fixed to its two ex- 



