CH. xii.] THE ELECTRICAL PHENOMENA OF MUSCLE. 139 



ic, is., one in which the tension remains constant throughout. If, on 

 the other hand, the muscle is fixed at both ends, and then excited, the 

 resulting activity expresses itself in a phase of increasing tension followed 

 by one of decreasing tension. If the alterations of tension are recorded, 

 we obtain what is called an isometric curve. This curve is obtained by 

 making the muscle pull against a spring which is so strong that the muscle 

 can only move it to a very slight extent. This slight movement is then 

 highly magnified. The curve thus obtained resembles in its main features 

 an isotonic contraction, but its maximum is reached earlier, and it returns 

 to the zero position sooner. The flat top of the isometric curve described by 

 the earlier observers was due to the imperfection of the instruments employed. 

 The tracings of muscle curves given in previous illustrations (see figs. 145 

 to 147) were obtained by the isotonic method, but it is probable that the 

 isometric curve is a more faithful record of the variations in the intensity 

 of the contraction process than that yielded by the isotonic method. The 

 momentum or swing of a light lever such as is used for obtaining isotonic 

 curves will no doubt account for the extra upward movement it executes. 

 The whole matter is under keen discussion at present, and the foregoing 

 view is that expressed by Kaiser. Schenk, on the other hand, maintains 

 what appears to be an improbable idea that there are really two kinds 

 of change in muscle, which account for the difference obtained by the 

 two methods. 



CHAPTER XII. 



THE ELECTRICAL PHENOMENA OF MUSCLE. 



WE have seen that the chemical processes occurring in muscular 

 contraction lead to a transformation of energy into work and 

 heat. These changes are accompanied by electrical disturbances 

 also. 



The history* of animal electricity forms one of the most 

 fascinating of chapters in physiological discovery. It dates from 

 1786, when Galvani made his first observations. Galvani was 

 Professor of Anatomy and Physiology at the University of Bologna, 

 and his wife was one day preparing some frogs' legs for dinner, 

 when she noticed that the apparently dead legs became convulsed 

 when sparks -were emitted from a frictional electrical machine 

 which stood by. Galvani then wished to try the effect of 

 lightning and atmospheric electricity on animal tissues. So he 

 hung up some frogs' legs to the iron trellis-work round the roof 

 of his house by means of copper hooks, and saw that they con- 

 tracted whenever the wind blew them against the iron. He 



* For a full and interesting account of this subject the reader is referred 

 to Professor M'Kendrick's " Text-book of Physiology," vol. i., chap, xviil 

 The account in the text is mainly a brief summary of this chapter. 



