XL v.] ELEGTKO-MOTIVE PHENOMENA. 23 1 



finger. The exjierimenter contracts the muscles, moving his middle finger 

 at a given rate, say once every two seconds, either by listening to the beat of 

 a metronome, or observing the motion of a pendulum vibrating a definite 

 number of times per minute. (A. Mosso, "Fatigue of human muscle," Du 

 Bois-Eeymond's Archiv, 1S90, and Uie Urmiidimg, Leipzig, 1892 ; Warren 

 P. Lombard, "Some of the influences which aff'ect the power of voluntary 

 muscular contraction," Journal of Fhysiology, xiii. i.) 



3. Dynamograph. — Waller has devised a simple fonn of this. 

 To the vertical arm of a dynamometer of Salter (p. 189), a strong 

 steel spring with a long recording arm is attached, the record 

 being made on a very slow-moving drum, e.g., a cylinder placed 

 vertically on the hour-spindle of an American clock. The 



iiynamograj)h is so arranged that it can be clamped to a table. The observer, 



by grasping the handles of the instrument, makes a series of maximal efforts. 



say 30 per minute, —i.e. , each lasting two seconds, — then he takes one minute's 



rest, and repeats the experiment. 



In this way one can measure the muscular strength and how it declines 



with each contraction or series of contractions, together with its recovery 



during rest. We have a series of isometric contractions. 



LESSON XLV. 



DIFFERENTIAL. ASTATIC GALVANOMETER— NON- 

 POLARISABLB ELECTRODES-SHUNT-DEMAR- 

 CATION AND ACTION-CURRENTS IN MUSCLE. 



ELECTRO-MOTIVE PHENOMENA OF MUSCLE 

 AND NERVE. 



1. Thomson's High-Resistance Differential Astatic Galvano- 

 meter. 



(a.) Place the galvanometer (fig. 155) upon a stand unaffected 



