THE STRUCTURE OF THE MOTOR ORGANS 89 



The Chemistry of Muscular Tissue. When we subject a mass 

 of muscle to chemical analysis we, of course, kill the fibers, if they 

 were not dead when the analysis was started. The difference be- 

 tween life and death is undoubtedly at bottom a chemical differ- 

 ence, so that we cannot hope by the ordinary methods of analysis 

 as applied to dead tissues to learn the exact chemistry of the living 

 muscles. On the other hand, the constituents we find in dead 

 muscle were derived from those of the living muscle, and are un- 

 doubtedly nearly related to them, so that knowledge of the chem- 

 istry of dead muscle cannot fail to give us a degree of insight into 

 the nature of the living muscle. 



To understand clearly the facts brought out by an analysis of 

 muscle we need to bear in mind that a muscle, as stated previously, 

 is an engine, whose property is to convert chemical energy into 

 mechanical. Our analysis will demonstrate the presence of some 

 substances which are part of the machinery; of others which make 

 up the fuel from which the energy for operation is derived; of still 

 others which are nothing more than the waste products from 

 previous activity. It is as though a locomotive in full career 

 suddenly fell into so deep a chasm as to reduce it with its tender to 

 a mass of indistinguishable fragments. Chemical examination of 

 the mass would bring to light various materials, such as steel, 

 brass, and nickel, which were part of the engine; coal, which was 

 the fuel; and ashes, representing the waste products. In similar 

 fashion we may pick out from a chemical study of muscle some 

 constituents which probably represent the machinery; others 

 which form the fuel; and still others which are waste substances. 



The most abundant single constituent of muscle is water, which 

 forms 75 per cent of its mass. Dissolved in the water are small 

 quantities of a number of simple inorganic salts, chiefly phos- 

 phates and chlorides of potassium, sodium, and magnesium. 

 Since experiment has shown that these salts, as well as the water 

 in which they are dissolved, are essential to the life and operation 

 of the muscle we may look upon them as part of the machinery. 

 Similarly the most abundant solid constituents of muscle, the pro- 

 teins, are to be included as portions of the mechanism. 



At least three proteins have been obtained from mammalian 

 striped muscle, myogen, an albumin, myosin, a globulin, both 

 coagulable by heat, and a protein which is insoluble in pure water 



