542 



MOVEMENTS. 



nerve 



curious experiments since made by Du Bois-Keyinond and others. One of the most sim- 

 ple methods of demonstrating this current is to prepare the leg of a frog with the crural 

 attached, and to apply one portion of the nerve to the deep parts of an incised 



muscle and the other to the 

 surface. As soon as the con- 

 nection is made, a contraction 



of the leg takes place> The 



same fact may be demonstrated 

 with an ordinary galvanometer ; 

 but the evidence obtained by 

 the frog's leg, when the experi- 

 ment is properly performed, is 

 sufficiently conclusive. 



Matteucci constructed out of 

 the fresh muscles from the thigh 

 of the frog, what is sometimes 

 called a frog-battery ; which ex- 

 hibits these currents in the most 

 striking manner, their intensity 

 being in direct ratio to the num- 

 ber of elements in the pile. To 

 do this, he takes the muscles 

 of the lower half of the thigh 

 from several frogs, removing 

 the bones, and arranges them in 

 a series, each with its conical 

 extremity inserted into the cen- 

 tral cavity of the one below. 

 In this way the external sur- 

 face of each thigh except the 

 last is in contact with the in- 

 ternal surface of the one below. 

 If the two extremities of the 

 pile be now connected with a galvanometer, quite a powerful current from the internal 

 to the external surface of the muscle may be demonstrated. In a pile formed of ten ele- 

 ments, the needle of a galvanometer was deviated to from 30 to 40. 



Electric currents are observed in all living muscles, but they are most marked in the 

 mammalia and warm-blooded animals. They exist, also, for a certain time after death. 

 Artificial tetanus of the muscles, however, instead of intensifying the current, causes the 

 galvanometer to recede. If, for example, the needle of the instrument show a deviation 

 of 30 during repose, when the muscle is excited to tetanic contraction, it will return so 

 as to mark only 10 or 15. This phenomenon is observed only during a continued mus- 

 cular contraction, and it does not attend a single spasm. 



Muscular Effort. The mere voluntary movement of parts of the body, when there 

 is no obstacle to be overcome or no great amount of force is required, is very different 

 from a muscular effort. For example, in ordinary progression there is simply a move- 

 ment produced by the action of the proper muscles, almost without our consciousness, 

 and this is unattended with any modification in the circulation or respiration ; but, if we 

 attempt to lift a heavy weight, to jump, to strike a powerful blow, or to make any vigor- 

 ous effort, the action is very different. In the latter instance, we prepare for the mus- 

 cular action by inflating the lungs, closing the glottis, and contracting more or less forci- 

 bly the expiratory muscles, so as to render the thorax rigid and unyielding ; and, by 



FIG. 161. Muscular current in the frog. (Bernard.) 



Fig. 1, portion of the thigh, with the skin removed; , surface of the 

 muscles ; &, section ; the direction of the current is indicated by the 

 arrow. 



Fig. 2, the nerve of a frog's leg (the leg enclosed in a glass tube) is ap- 

 plied to the section and the surface of the muscle. There is no contrac- 

 tion, because it is necessary that a portion of the nerve should be 

 raised up. 



Fig. 8, a portion of the nerve is raised with a glass rod. The contraction 

 of the galvanoscopic leg occurs at the making of the circuit, because 

 the current follows the course of the nerve, or is direct. 



Fig. 4, the contraction here occurs at the breaking of the circuit, because 

 the direction of the current is opposite the course of the nerve, or is 

 inverse. 



