146 THE ELECTRICAL PHENOMENA OF MUSCLE. [CH. XII. 



Lippmann's Capillary Electrometer. This instrument is often used 

 instead of the galvanometer. It consists of a glass tube drawn out at one 

 "-i 1 to a fine capillary and filled with mercury. It is connected to an 

 apparatus by which the 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 ; 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 sensi- 

 tive photographic plate, photographs are obtained which show the electrical 

 variations in a living tissue in a graphic manner. The instrument is exceed- 

 ingly 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 

 (i, i, i, i), one in the galvanometer circuit (2. 2, 2, 2). The bar revolves. 

 and by making or breaking the primary circuit sends an induction shock 

 into the nerve at the same instant. 



The muscle is connected by non-polarisable electrodes to the galvano- 

 meter ; this circuit includes the brass blocks 2, 2, on the disc over which the 

 bar revolves, and a compensator not shown in the figure to neutralise any 

 current set up by the muscle in a state of rest. If an electrical change 

 occurs in the muscle, it is only noticed by the galvanometer if at the same 

 time the bar on its revolution connects the two brass blocks on the disc, and 

 so completes the circuit. The apparatus can be set so that the bar makes 

 the primary contact (i, i) simultaneously with the galvanometer contacts, 

 or that the galvanometer contact is made, I, 2, 3, &c. hundredths of a second 

 later than the primary contact. If the two are closed simultaneously the 

 electrical condition of the muscle is tapped off at the moment of excitation ; 

 if the galvanometer contact is closed ^ ^ ^, &c. second after excitation, 

 the electrical condition of the muscle at that particular instant is ascertained. 

 By a number of experiments with different intervals between the making 

 of the two contacts, one ascertains how long after the excitation the change 

 in the electrical condition of the muscle takes place. 



We can now pass on to a consideration of results. 



In muscles that are removed from the body, it is found that 

 on leading off two parts of their surface to a galvanometer, the 

 galvanometer needle generally swings. The most marked result 

 is obtained with a piece of muscle in which the fibres run parallel 

 to one another, and the longitudinal surface is connected with one 

 of the cut ends by a wire (2 in fig. 170). 



On the course of the wire a galvanometer indicates that a 

 current flows from the centre to the cut end outside the muscle, 

 and from the cut end to the centre inside the muscle. If, now, 

 the muscle is thrown into tetanic contraction, the needle returns 

 more or less completely to the position of rest. 



Du Bois Reymond, who first described these facts, called the 



