i GENERAL PHYSIOLOGY OF MUSCLE 61 



Baudin has recently carried tlie construction of mercury thermometers with 

 small bull >s for physiological purposes to such perfection that he has obtained 

 a scale in which each degree is divided into fifty parts. But even with an 

 ordinary clinical thermometer, divided into tenths of a degree, it is possible 

 on reading the scale under the microscope to estimate differences of a hundredth 

 of a degree. 



The thermo-electric method has, as compared with the thermometric 

 method, the great advantage of almost instantaneously indicating rapid 

 alterations in the temperature of the muscle. On the other hand it is more 

 difficult and delicate of application, and may lead to fallacies if not employed 

 very cautiously. 



The thermo-electric method is founded on the following principle : If two 

 different metals united by two junctions are included in the circuit of a 

 low resistance galvanometer, the heating or cooling of one of the junctions 

 gives rise to an electric current, which deflects the needle of the galvanometer 

 in the positive or negative direction, in proportion with the rise or fall of 

 temperature in the first junction, if that of the second remains unchanged. 

 To investigate muscular therniogenesis it is best to take needle-shaped 

 thermo-electric couples (Fig. 38), which are plunged into two symmetrical 

 muscles of the frog, one of which is at rest, the other contracting (Helmholtz). 



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FIG. 39. Photograph of positive and negative variations of temperature obtained with two 

 thermo-electric needles pushed into the two gastrocnemius muscles of a frog, and connected 

 with a low resistance galvanometer ; the sciatic nerve was excited alternately on either side. 

 (A. D. Waller.) The excursions of the galvanometer mirror are photographed by a beam of light 

 reflected on to the sensitive surface of a moving drum. Each tetanising excitation of the 

 sc-iatics, respectively, lasted one minute as indicated by the break of the abscissa line. During 

 tetanus the curve falls or rises, according as the right or left sciatic was excited. 



To measure the rise of temperature developed in a simple twitch a Melloni's 

 thermopile is used, which consists of several elements, the two muscles of 

 the frog being placed in contact with the two surfaces at which are the 

 junctions of the elements of the pile (Heidenhain). 



If a mirror is attached to the magnet of the galvanometer, its deflections 

 can be photographed by the reflection of a ray of light upon a sensitive 

 surface (Waller, Fig. 39). 



The first experiments that proved incontestably that muscle 

 is concerned in the production of heat as well as motion were 

 performed on cold-blooded animals by Helmholtz (1847). By 

 employing the thermo-electric method he saw that the muscles of 

 the frog's thigh developed heat during indirect or direct tetanisa- 

 tion (0-14-0-18 C.). 



In later experiments (1864) Heidenhain measured the rise of 

 temperature (1-5 hundredths of a degree) in the isolated gastro- 

 cnemius of the frog after a simple twitch. 



There is therefore no doubt that muscular contraction is 

 accompanied by a development of heat, which is due to an increase 

 of exothermal processes within the contractile organ, by which the 

 greater part of the store of accumulated energy is dispersed. 



