398 THE PROPERTIES OF STRIPED MUSCLE. 



It was one of the great discoveries of Helmholtz, that when a muscle 

 is tetanised its temperature increases. The method of measuring this 

 increase, and of determining its relation to the other phenomena of the 

 excitatory state, was subsequently elaborated by Heidenhain. 1 



Methods. — It need scarcely be mentioned here that both of these great 

 observers used the thermo-electric method. Heidenhain employed a small 

 thermopile specially made for the purpose, of fifteen bismuth and antimony 

 couples, of which one set of junctions was covered by the muscle to be 

 investigated (the gastrocnemius of the frog), while a dead muscle was similarly 

 applied to the junctions on the opposite side of the thermopile; and this, 

 when the method is carried out in accordance with his directions, is 

 found to be abundantly sensitive for its purpose. But this very sensitive- 

 ness brings the observer face to face with great technical difficulties ; for 

 it is found that even if two inactive muscles are compared with each 

 other by applying them severally to the opposite sides of the thermopile, 

 it is extremely difficult, even when the instrument is kept in a "moist 

 chamber " and protected from changes of temperature in the environment, 

 to bring the needle to a fixed position. As no observations can be made 

 until the accidental disturbances which prevent this have been got rid of, 

 much time is unavoidably lost. Nor is this the only practical objection to the 

 method, for it has further to be borne in mind in dealing with the result, that 

 what is measured is not the temperature of the muscle itself, but that of the 

 junctions, because, from the form of the thermopile, these cannot be brought 

 into such proximity to the muscle that the two temperatures can be considered 

 the same. These considerations induced Fick, 2 more than twenty years 

 ago, to give to the thermopile such a form that, although the instrument is 

 rendered less sensitive, it affords more reliable indications of the changes which 

 occur in the muscle. Fick's thermopile consists of very slender strips of iron 

 and German silver. The end of each strip is filed away on one side, and is 

 soldered to its fellow in such a way that the surface of junction of the two 

 ends does not extend more than half a millimetre. As their united ends are as 

 thin as paper, their mass is so inconsiderable that they assume the temperature 

 of the muscular substance by which they are surrounded, without altering it. 

 The end of this thermopile resembles a comb of six teeth, each of which is a 

 junction ; its form renders it possible to introduce it betAveen the fibres of a 

 muscle with very little injury ; it is, however, more advantageous to avoid all 

 risk of this kind by introducing it between the tAvo adductor groups of muscles 

 (Fig. 189) placed abreast of each other. These, Avhen properly arranged and 

 excited simultaneously, apply themselves by their opposed internal surfaces to 

 the junctions as perfectly as if its knife-like edge Avere plunged into the 

 muscular substance. Whatever form of thermopile is used, it must be 

 graduated. The data for graduation are — (1) The deflection obtained Avith a 

 larger element of the same material as that used in making the thermopile, 

 Avith a known resistance in circuit and a knoAvn (considerable) difference of 

 temperature betAveen the junctions; and (2) the resistance of the thermopile 

 circuit, as actually used for measurement. 



Relation between thermogenetic and inogenetic processes.— 

 Before proceeding to the discussion of the influence of physiological and 

 other conditions on the production of heat in a contracting muscle, it 

 will be useful to set forth the general results of experiments as to the 



1 ' ' Mechanische Leistung, Warmeentwickelung u. Stoffumsatz Lei der Muskelthatigkeit," 

 Leipzig, 1864, S. 63. 



2 " Ueber die Warmeentwickelung bei der Muskelzuckung," Arch. f. d. ges. Physiol, 

 Bonn, 1877, Bd. xiv. S. 31. 



