THE MUSCULAR MOTOR AND ALIMENTATION 121 



mum. This law is instinctively ot served, thus a workman who 

 pushes a wheelbarrow holds it without bending his arms more 

 than is necessary. 



85. Besides the woik of the muscle in displacing the weight P, 

 the shortening takes two limiting values, r and r', to which the 

 forces of contraction, F and F' correspond ; so that the force has 



F 4- F x 



an average value, = F w . Replacing F by P (1 -f r) 



andF'b^P (1 + r') : 



F = 



r +r 



F-) 



The dynamic contraction accomplishes work of which the 

 factors are : the average shortening, and the average force F///. 

 According to whether the work is " positive " or " negative " the 

 average effort increases or diminishes slightly, by a quantity not 

 fixed " a priori." ( l ) The examination of photographs of active 

 muscles has revealed to Mr. Paul Richer that they are distended 

 to varying degrees according to the motor, or resistant character, 

 of the contraction. 



Chauveau verified the laws of elasticity, or rather of muscular 

 contraction, experimentally by causing a man to hold a weight 

 with the forearm bent upon the arm, and by modifying the degree 

 of flexion as well as the value of the weight. ( 2 ) The results 

 obtained were satisfactory ; more so than those obtained by 

 Dondus and Van Mansvelt.( 3 ) 



It is interesting to recall certain observations made by 

 Winslow ( 4 ) in the year 1720. He remarked that the increased 

 distension ot the biceps with increase in the flexion of the arm, and 

 the weight supported, could be readily felt. If the arm was bent 

 to a definite degree and then fixed in that position and held so that 

 the flexoi muscles were entirely relaxed and exerted no effoit, and 

 then an additional stress was applied, tfce muscles would be pro- 

 portionately distended, although no movement took place at the 

 elbow joint. The action differed from that of a spring under 

 compression or tension. 



The researches of Dondv*s and of Chauveau were on the pre- 

 ceding lines. 



86. According to the laws of elasticity muscular deformation is 

 proportional to the length ot the muscle. A bone capable of 



(*) A. Chaveau (Journal de Physiologic , 1900, p. 313. 



( 2 ) The apparatus is described by Tissot in the Journal de Physiologic, 

 1899, p. 18L 



( 3 ) Dondus and Van Mansvelt, Over de Elasticitat dev Spier en, Utrecht 

 1863. 



(*) Winslow (Mem. Acad Roy. d. Sciences, 1720, p. 87). 



