138 



THE ELECTRICAL PHENOMENA OF MUSCLE 



[GIL XII. 



neutralise the muscle current ; if c is half way between a and />, half the Daniell's 

 strength will be sent in ; but this is also too much ; ac will be found to be only 

 quite a small fraction of ab ; and this fraction will correspond to a proportional 

 fraction of the electromotive force of the Daniell cell. 



Lippmann's Capillary Electrometer. This instrument is often used instead 

 of the galvanometer. It consists of a glass tube drawn out at one end to a fine 

 capillary and filled with mercury. It is connected to an apparatus by which the 



FIG. 167. Frog's heart. Diphasic variation. Simultaneous photograph of a single beat (upper black 

 line), and the accompanying electrical change indicated by the level of the black area, which shows 

 the varying level of mercury in a capillary electrometer. (Waller.) 



pressure on this mercury can be lowered or increased. The open capillary tube is 

 enclosed within another tube filled with 10 per cent, sulphuric acid. Two platinum 

 wires fused through the glass, pass respectively into the mercury and the acid, and 

 the other ends of these wires are connected by electrodes to two portions of the 

 surface of a muscle. The capillary tube is observed by a microscope (see fig. 166). 

 The surface of the mercury is in a state of tension which is easily increased or 

 diminished by variations of electrical potential, and the mercury moves in the 

 direction of the negative pole. 



If the shadow of the mercurial column is thrown upon a travelling sensitive 

 photographic plate, photographs are obtained which show the electrical variations 



FIG. 1(38. Human heart. Diphasic variation, KE, and simultaneous cardiogram, cc. Time it is 

 marked in ^th second. The lead-offs to the capillary electrometer were from the mouth to the 

 sulphuric acid, and from the left foot to the mercury. (Waller.) 



in a living tissue in a graphic manner. The instrument is exceedingly sensitive, 

 and its indications are practically instantaneous. Figs. 167 and 168 indicate the 

 kind of result one obtains with the heart, which will be more fully discussed when 

 we are considering that organ. 



The Rheotome. This is an instrument by means of which the time of the 

 occurrence of electrical disturbances in relation to the contraction of a muscle can 

 be determined. This is in principle effected by a revolving bar carrying two contacts, 

 one in the primary or exciting circuit (1, 1, 1, 1), one in the galvanometer circuit 



