on the Motion uj f he Arm. 4 17' 



diseases which have similar cerebral effects. From these and 

 some other facts adduced, he infers that cerebral influence on 

 the one hand, and certain qualities of the muscular' tissue itself 

 on the other, are the two elements of muscular contractility. 



Mayo has indicated a method of determining the maximum 

 strength of individual muscles, by ascertaining the weight that 

 is required to rupture their tendons. This mode is founded 

 upon the argument that the tension which the tendon can 

 sustain, probably exceeds but little that which the fibres can 

 exert; a supposition which is analogically probable, and in 

 some measure supported by facts, since in praeternatural con- 

 traction sometimes the tendon, sometimes the trunk, of a 

 muscle gives way* ; proving that there is no great difference 

 between the active and passive strength of these organs. 



The constant and equable stream of galvanism, afforded by 

 Daniell's new battery, will furnish, I think, a good means of 

 comparing the strength of muscles, of regular shape and equal 

 size, by ascertaining the contractile force it induces in its pass- 

 age through each. 



In order to subject any muscle to this experiment, it should 

 be separated from its fellows, and, at the distal end, from its 

 insertion. By the tendon, thus detached, it should be con- 

 nected with a spring moving an index ; and the bone, into 

 which its opposite extremity is inserted, should be firmly fixed 

 at a known distance from the spring. The trunk of the muscle 

 .should then be made part of the circuit ; and the distance to 

 which it moved the index during the transmission of the cur- 

 rent for a given period (say one minute) might be taken to 

 express the force of the muscle as compared with others sub- 

 mitted to the same treatment -f-. 



The comparative dimensions and weight of such muscles 

 as resemble each other in colour, firmness, and texture, would 

 also probably bear some proportion to their comparative force. 



Although neither of these methods of estimating muscular 

 contractility could be depended on alone, yet by a judicious 

 application of each in turn, to corroborate or correct the re- 

 sults furnished by the others, a close approximation might at 

 last be obtained. And since we have proof that there is an 

 accurate balancing of muscular force in the fact that muscles, 

 or sets of muscles working together, are fatigued, equally and 

 simultaneously, we may fairly expect that u iiatever the ab- 



• See Tetanus Cooper's First Lines of Surgery. 



t Tlie contraction of tiie uuiscle only occurs at the instants of com- 

 pleting and interrupting tlie circuit. Contact must therefore be broken 

 arid renewed at regular intervals during the experiment; which is readily 

 cflTected by means of a pendulum coimected with the wire. See Bec- 

 fjuerel's Trailc dc r Eleclricite, vol. iv. p. .'{OH. 



'J7)irrf Srr/rs. Vol. 9. No. rifi. I)rc. IH'AG. .'i D 



