372 THE HUMAN MOTOR 



285. Crawling. This method of locomotion is a progression 

 on hands and knees. Owing to the fact that the inflexions of the 

 vertebral column ( l ) are numerous certain therapeutic applica- 

 tions have been made of it. Crawling is very troublesome, and 

 is not to be recommended either in games or in military exercises, 

 unless absolutely necessary. It gives rise to callous formations 

 on those parts which constantly rub on the ground. 



286. Swimming.) 2 ) As swimming is a mode of progression used 

 principally in sport and recreation, and not in industry, it will 

 not be examined in any detail here. The effect of environment 

 is of the first importance. This environment, the water in which 

 the swimmer is immersed, is of approximately the same specific 

 gravity as the human body. The swimmer floats on his back 

 because the Centre of Gravity of his body is nearer to his back 

 than his front. He maintains his position by movements of the 

 arms from below upwards, as also by inflation of his lungs ( 178). 

 If he lifts his head entirely out of the water he sinks. His feet 

 touch the bottom and the body remains in an inclined position. 



In swimming the legs are alternately bent and straightened, the 

 soles of the feet exerting a thrust against the water. The arms 

 describe lateral circles, the hands acting like paddles. 



The muscular energy exerted in swimming is considerable, the 

 more so if there is any current of the water opposing the swimmer's 

 progress ( 178). The temperature of the water also may cause 

 considerable loss of heat energy and, altogether, the expenditure 

 of energy in swimming is very high. 



The famous swimmer, Burgess, crossing the Channel between 

 Cape Gris-Nez and Dover, took 23 hours 40 minutes to cover 

 about 36-200 km., or 1-53 km. an hour. Though, owing to devia- 

 tions from the. straight course, he claims to have attained a speed 

 of 2-800 km. an hour ( 3 ) and it may be remembered that at Join- 

 ville le-Pont five years before, he covered 44 kilometres in 24 

 hours, or 1-860 km. an hour. 



At an average speed of 1-800 km. and against a current of 2 

 metres, the work done per hour rises to : 



73 X 0-035 X 2^50 2 x 1,800 = 28,734 kilogrammetres. 

 a power of about 8 kilogrammetres per second. 



(*) Klapp (Munsch. Med. Wochensch., vol. lii., No. 48, p. 2311, 1905). 



( a ) R. Thomas, Swimming, London, 1904. 



() Le Matin of 7th September, 1911, completed by Le Temps of the same, 

 day. (Burgess consumed on the journey chocolate and soup, but no 

 alcohol) . 



