The Muscular System. 251 



the explanation of the value of hand-rubbing the legs of 



Great difference of opinion exists as to whether fatigue 

 begins in the nervous system or in the muscles themselves. 

 I incline to the view that the nervous system fails first. 



That remarkable state of the body described as ' condi- 

 tion,' into which horses can be brought by care in feeding 

 and general management, and carefully-regulated work, 

 must be regarded as the highest pitch of perfection into 

 which muscles can be brought ; it is not a permanent con- 

 dition : no horse can remain in it for any length of time, and 

 many can never be got into it at all. It is easy in the train- 

 ing of horses to overstep the mark and produce ' stale- 

 ness,' a condition due to over- training, but which, unless 

 it be gone too far, is in both men and horses recovered from 

 by a short judicious rest, when the system immediately 

 responds. ' Staleness ' must be regarded as having its 

 primary origin in the nervous system. 



Laws of Muscular Work. — The material used up in muscle 

 as the result of contraction may be regarded as so much 

 fuel. Looked at from this point of view the muscles are 

 very superior machines, for they obtain from the fuel one- 

 fourth the amount of energy it is capable of producing, 

 whereas the best-made and most carefully-constructed 

 engine, cannot extract from fuel more than one-ninth the 

 energy it is capable of yielding ; moreover, the animal 

 machine gets stronger by wear instead of weaker. 



The amount of work performed by the body is measured 

 in foot-tons, viz., the number of tons lifted 1 foot high. It 

 is evident that the force which can lift 1 ton 20 feet high 

 would be equivalent to the force which lifts 20 tons 1 foot 

 high (see Locomotion). 



The work performed by a muscle is ascertained by multiply- 

 ing the weight lifted by the height to which it has been lifted. 



The following are the laws of muscular work : 



1. The larger the transverse section of a muscle, the 

 greater the load it can lift. 



2. The longer the muscle, the greater the height to 

 which it can lift a load. 



