4i8 



THE PROPERTIES OF STRIPED MUSCLE. 



must be guided in interpreting them. The data in question are, as most 

 readers now know, curves obtained by projecting the image of the 

 mercury column of an electrometer (Fig. 230) on to a photographic plate, 

 which moves at an equable rate behind a slit. The instrument takes the 

 place of the galvanometer and shunt, in the circuit represented in Fig. 

 223, 1 the electrode on the injured end of the muscle, marked d in that 

 figure, being supposed in the following paragraphs to be connected 



with the capillary, and that on the 

 muscular surface, marked pr, with the 

 sulphuric acid ; the current of a muscle 

 injured at one end and placed as shown 

 in the figure, would therefore be indicated 

 by a movement of the meniscus from 

 the point of the capillary. The shadow 

 of a vibrating prong of a tuning-fork 

 falls on the same plate at the same time, 

 so that the time-relations of the move- 

 ments of the meniscus of the mercurial 

 column can be measured ; and, by an 

 automatic arrangement, the moment at 

 which the circuit of the primary coil of 

 the inductorium which serves to excite 

 the muscle preparation, is opened, is also 

 shadowed on the plate. The discovery 

 which furnished the key to the inter- 

 pretation of the curves so obtained, as 

 indicating the nature and time-relations 

 of the almost instantaneous electromotive 

 changes we have now under consideration, 

 was made by Mr. G. Burch, in the course 

 Fig. 230.— Bm-cli's projecting elec- of experiments carried out in the Oxford 

 trometer. The shorter limb Physiological Laboratory, the results of 

 of the wide tube contains a which w communicated to the Eoyal 



piece of thick walled tube c, . J 



which is ground in like a society m 1892/ He showed that the 

 stopper. The front of this difference of potential at the moment 

 tube is ground away so that corr esponding to any point in such a 



its bore is laid open from end r . ■,,•■,•.• , 



to end, forming a trough wide curve of electrical variation, can be 



enough tocontain the capillary, readily estimated from quantities which 



A thm coyer glass closes the ma „ ^ e determined by the examination 



trough in front, which is kept „ J , . ,» J , . , m, 



full of liquid by the surface of the curve itself at that point. These 



are — (1) The distance through which the 

 meniscus has moved from its zero position, 

 and (2) the inclination of the curve 

 representing the velocity of the mercury, 

 at the particular moment. Each of these quantities has its value 

 in positive or negative difference of potential. To estimate their 

 values, another curve must be obtained by photographing the excur- 

 sion when a known difference of potential (say of - 01 volt), derived 

 from the compensator, is allowed to act on the electrometer, so as 

 to determine a movement of the mercury towards the point of the 



1 If it is desired to use the galvanometer at the same time, the electrometer may be 

 connected with k 4 . 



8 Burch, Phil. Trans., London, vol. clxxxiii. p. 81. 



tension of the acid. For 

 further description see "The 

 Capillary Electrometer," 

 London, 1896. 



