CHAP. IX.] THE CONTRACTILE TISSUES. 345 



Maximum The maximum work done under most favourable 



work. conditions is said to vary between about 3500 and 5500 



gram-meters per gram of frog-muscle 1 . 



Heat of Con- The mechanical motion of contraction is not the 



tracting only exhibition of kinetic energy which accompanies 



Muscle. t^ chemical changes of acting muscle. During tetanus 2 



and in single contractions 3 , the muscles become raised in temperature ; 

 and since this occurs in muscles removed from the circulation or 

 even in muscles entirely removed from the body, it must be due 

 to the heat-developing processes of the tissue itself. 



Helmholtz, in a 2 3 minutes-tetanus through nerves, found the 

 thigh of a frog raised '14 to "18 C. ; and Heidenhain observed the 

 temperature of the gastrocnemius to be raised '001 to '005 C. in 

 a single contraction. 



If the weight of the gastrocnemius be known, and also the specific 

 heat of muscular tissue, it is possible to estimate in heat-units the amount 

 of heat generated in one contraction. Fick 4 , taking the specific heat 

 of muscle to equal that of water, found that in one energetic contraction, 

 under most favourable conditions for activity, every gram of the contracting 

 muscle generates heat enough to raise 3'1 mgr. of water through 1 C. 

 The specific heat of muscle is however stated to be '7692 by Adamkiewicz 5 , 

 and -825 by Eosenthal 6 . 



The evolution of heat in contraction is amenable to the same 

 influences as the evolution of mechanical work ; but though amen- 

 able in the same sense it is not so in the same degree. Thus, as the 

 stimulus gains in strength, not only does the lift become higher, 

 but the heat liberated is also increased, with this difference, that 

 the heat evolved is increased more rapidly than the lift 7 . So also the 

 greater the tension of a muscle, whether before or during contraction, 

 the greater, within bounds, will be the heat evolved as well as 

 the work done ; but here again, as the tension increases, the heat 

 evolved reaches a maximum and begins to decline sooner than 

 the mechanical effect 8 . 



1 Hermann's Handbuch, Bd. i. Abth. i. p. 79. 



2 Bunzen in Gilbert's Annalen, 1807, vol. xxv. p. 157 : quoted in Heidenhain, Mecha- 

 nische Leistung, etc., p. 33, where also will be found an account of the earlier researches 

 in which the heat of the body, and of muscles within the body, was found to be in- 

 fluenced by exercise. Helmholtz, " Ueber die Warmeentwicklung bei der Muskelaction. " 

 Arch. f. Anat. Physiol. u. tviss. Med. (Miiller), 1848, p. 144. 



3 Heidenhain, Mechanische Leistung, Warmeentwicklung und Stoffumsatz bei Mus- 

 kelthdtigkeit. Leipzig, 1864, p. 73. 



4 Fick, "Ueber die Warmeentwicklung bei der Muskelzuckung." Pfliiger's Archiv, 

 Vol. xvi. p. 84. 



5 Adamkiewicz, "Die Warmeleitung des Muskels." Arch. f. Anat. Physiol. u. wiss. 

 Med. (Eeichert and du Bois-Eeymond), 1875, p. 254. 



c Rosenthal, "Ueber die specifische Warme thierischer Gewebe." Monatsber. d. 

 Berliner Acad., 1878, p. 307. 



7 Nawalichin, " Myothermische Untersuchungen." Pfliiger's Archiv, Vol. xiv. 

 p. 295. 



8 Heidenhain, Mechanische Leistung, etc. p. 84 et seq. 



