CTT. XT.] 



MUSCULAR WORK 



131 



gramme-millimetres, the next 20x6 = 120 gramme-millimetres, and 

 so on, while the last on the right, 100 x 3 = 300 gramme-millimetres. 

 It is thus seen that the height of a muscle-curve is no measure of the 

 work done by the muscle unless the weight lifted is taken into 

 account as well. 



The following figures are taken from an actual experiment done 

 with the frog's gastrocnemius (Weber) : 



FIG. 159. Dynamometer. 



The work increases with the weight up to a certain maximum, 

 after which a diminution occurs, more or less rapidly, according as 

 the muscle is fatigued. 



Similar experiments have been made in human beings, weights 

 being lifted by the calf muscles, or elbow muscles, leverage being 



allowed for. In the higher g$ 



animals the energy so ob- 

 tained compared with the frog 

 is about twice as great for 

 the same volume of muscular 

 tissue. 



Fig. 159 represents a com- 

 mon form of dynamometer for 

 clinical use, employed in test- 

 ing the muscles of the arms 

 and hands. It is squeezed by the hand, and an index represents 

 kilogrammes of pressure. 



The muscle, regarded as a machine, is sometimes compared to 

 artificial machines like a steam-engine. A steam-engine is supplied 

 with fuel, the latent energy of which is transformed into work and 

 heat. The carbon of the coal unites with oxygen to form carbonic 

 acid, and it is in this process of combustion or oxidation that heat 

 and work are liberated. Similar, though more complicated, combus- 

 tions occur in muscle. In a steam-engine a good deal of fuel is con- 

 sumed, but there is great economy in the consumption of the living 

 muscular material. Take the work done by a gramme (about 15 

 grains) of muscle in raising a weight of 4 grammes to the height of 

 4 metres (about 13 feet) ; in doing this work probably less than a 

 thousandth part of the muscle has been consumed. 



Next let us consider the relationship between the work and the 



