98 PHYSIOLOGY OF MUSCLE AND NERVE 



By equipping this indicator with a small mirror, a beam of light may be reflected 

 from it upon a screen or into a photographic camera. Its excursions are standard- 

 ized with the help of a very sensitive thermometer. 



Becquerel and Bichet (1835) who first employed this method upon the biceps 

 muscle of a human subject, obtained a rise of 0.5° C. during energetic movements. 

 In a similar way, Helmholtz (1847) has found that the tetanization of a frog's mus- 

 cle raises its temperature 0.14-0.18° C, while Heidenhain^ has noted a rise of 

 0.005° C. during single contractions. It must be remembered, however, that even 

 a resting muscle serves as a thermogenic organ, because the blood returned from 

 it possesses a higher temperature than that passing into it (Ludwig, 1881). In 

 addition, it has been ascertained that the heat production varies directly with the 

 intensity of the chemical changes. A strong stimulus, therefore, must yield more 

 heat than a weak one. Tension has a similar influence, because isometric contrac- 

 tions are followed by a greater liberation of heat than isotonic. Weight acts favor- 

 ably at first, on account of its initial tendency to augment the mechanical energy; 

 later on, however, the liberation of heat diminishes more rapidly than the amount 

 of work. These and other facts tend to show that a muscle works more economic- 

 ally when acting against a moderate load than when not weighted at all. Further- 

 more, when a fresh muscle and a fatigued muscle are made to perform the same 

 amount of work, the former generates more heat than the latt^, because it is 

 in possession of a greater store of chemical substances. 



The Muscle as an Electrogenic Organ. — The electrical current 

 generated by a battery finds its origin in chemical changes enacted by its 

 constituents. In quite the same way, the diflferences in electrical poten- 

 tial developed by muscle and other forms of protoplasm, find their 

 cause in chemical alterations accompanying their activity, and hence, 

 are derived from their stored potential energy. The amount of elec- 

 trical energy developed by muscle is rather small, but it should not be 

 forgotten that this amount is considerably augmented by the sum 

 total of the electricity which is evolved by the glands, nervous struc- 

 tures and other tissues. The final result, therefore, is far from trivial. 



It need scarcely be mentioned that certain animals, for example, the electric 

 fish, possess special organs for the generation of this form of energy to serve as 

 a weapon of offense and defense. It is stated that Malapterurus electricus inhabit- 

 ing the rivers of Africa (Nile), is capable of producing a shock equalling 200 volts. 

 The organ itself is situated directly below the skin on each side of the body and 

 consists of a number of membranous plates arranged parallel to one another. In 

 Gymnotus and Malapterurus these plates are placed vertically and in the Torpedo 

 horizontal to the long axis of the body. Each organ is innervated by a nerve which 

 subdivides and sends branches to each plate. In Malapterurus this nerye is but a 

 single giant fiber possessing a very thick investment and derived from a single 

 large ganglion cell. The long discussions, whether these electrical organs consist of 

 modified muscle or nerve tissue or whether they are embryologically distinct, have 

 led to the conclusion that those of Torpedo and Gymnotus have been derived 

 from muscle tissue, while that of Malapterurus is an outgrowth of the skin glands. 



Schonlein has estimated the electromotive force of an entire organ of the Tor- 

 pedo at 0.08 volt for each plate; hence, it equals that of thirty-one Daniell cells. 

 This voltage is sufficient to kill other fish and animals and especially because it is 

 discharged in transverse lines. The discharge results chiefly in a reflex manner up- 

 on mechanical stimulation. In Malapterurus the shock traverses the conductor 

 in a direction from the head to the tail of the animal and in Gymnotus from the 



1 Mechanische Leistung, etc., Leipzig, 1864; also see: Fick, Myotherm. Unter- 

 Buchungen, etc., Wiesbaden, 1889. 



