480 



MOVEMENTS VOICE AND SPEECH. 



may also be demonstrated with an ordinary galvanometer ; but the evidence 



obtained by the frog's leg is sufficiently conclusive. 



Matteucci constructed out of the fresh muscles from the thigh of the frog, 



what is sometimes called a frog-battery; which is made by taking the 



muscles of the lower half 

 of the thigh from several 

 frogs, removing the bones, 

 and arranging them in a 

 series, each with its coni- 

 cal extremity inserted into 

 the central cavity of the 

 one below. In this way 

 the external surface of 

 each thigh except the last 

 is in contact with the in- 

 ternal surface of the one 

 below. If the two extrem- 

 ities of the pile be con- 

 nected with a galvanome- 

 ter, quite a powerful cur- 

 rent from the internal to 

 the external surface of the 



FIG. 157. Muscular current in the frog (Bernard). muscle may be demon- 



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

 the muscles ; 6, section ; the direction of the current is indi- 

 cated by the arrow. 



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

 applied to the section and the surface of the muscle. There is 

 no contraction, because it is necessary that a portion of the 

 nerve should be raised up. 



Fig. 3, a portion of the nerve is raised with a glass rod. The con- 

 traction of the galvanoscopic leg occurs at the making of the 

 circuit, because the current follows the course of the nerve, or 

 is descending. 



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 ascending. 



T n ,-.il fn rrn orl 

 Ill d pll 



OI ten elements, tlie nee 



f ll ^f Q 0-al^mnr.mofor wao 

 c 



HP via tori 30 +n J.0 

 L 



TTlonfrin nnrronfs QT-P 

 observed m all living H1US- 



cleS but thev are most 

 J 



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 cur- 

 rent, 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, or it may 

 even return to zero. This phenomenon, which is called negative variation of 

 the muscular current, is observed only during a continued muscular contrac- 

 tion and it does not attend a single contraction. 



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

 when there is no obstacle to be overcome or no great force is required, is 

 very different from a muscular effort. For example, in ordinary progression 

 there is simply a movement produced by the action of the proper muscles, 

 almost without consciousness, and this is unattended with any considerable 

 modification in the circulation or respiration; but in attempting to lift a 

 heavy weight, to jump, to strike a powerful blow or to make any vigorous 



