GENERAL PHYSIOLOGY OF MUSCLE AND NEBVE. 165 



of rigor caloris. The heated muscle may, therefore, be the .seat of three 

 different kinds of processes, each of which leads to a shortening. If frog's 

 muscle be gradually heated, it shows three separate contraction movements 

 at three separate temperatures, at about .'34°, 47°, 58° C. The last two con- 

 tractions are due to heat coagulation of paramyosinogen (myosin of v. 

 Furth) at 47° C, and myosinogen (myogen of v. Furth) at 58° C. These 

 are undoubted effects of heat rigor. There is a difference of opinion as to the 

 nature of the first contraction. It has been generally attributed to the 

 coming on of rigor mortis — i. c, to a post-mortem coagulation of para- 

 myosinogen and myosinogen. In case a muscle be rubbed between the 

 fingers, so that its anatomical condition is altered, although the chemical 

 structure remain the same, this form of shortening does not occur, and it is 

 not until the temperatures at which paramyosinogen and myosinogen are 

 coagulated by heat are reached that the muscle begins to shorten. 1 Probably 

 the rigor-mortis change occurs, but on account of the physical change in the 

 fibre it does not reveal itself. This suggests the well-known fact, that when 

 the rigidity of a muscle in rigor has been broken up by mechanical means it 

 does not return. The condition of the muscle has an important influence on 

 the temperature at which it will enter into rigor when heated. Latimer 2 

 reports that a fatigued muscle will go into rigor at a temperature 10 degrees 

 lower than a fresh muscle will. Probably both fatigue and high tempera- 

 ture are favorable to the formation of the myosin ferment, and heat hastens 

 the fermentation process, resulting in coagulation. Another view of the 

 nature of the first form of contraction has been advanced lately. According 

 to Brodie and Richardson, 3 this contraction in the case of frog's muscle may 

 be very considerable, and is due to heat coagulation of soluble myogen fibrin, 

 a form of proteid which v. Furth found to be formed from myosinogen (what 

 he termed myogen) at 30° C. Mammalian muscles do not show any marked 

 contraction at this temperature, and have not been found to contain myogen 

 fibrin. This form of shortening is seen only by light loads, for the coagula- 

 tion of the proteids of the muscle causes increased extensibility, in addition 

 to the tendency to contract. 1 The change of form in rigor caloris is more 

 in voluntary than in involuntary muscles, as much as 60 per cent, in the 

 former and 10 per cent, in the latter. The beginning of heat-rigor comes 

 at very different temperatures in the different muscles of different animals. 

 Mammalian muscle can stand several degrees higher than the muscles <>f 

 cold-blooded animals, heart-muscle can be heated two or three degrees higher 

 than the skeletal muscles, and skeletal muscles differ, e. g., the semimem- 

 branosus of the frog enters into rigor sooner than the gastrocnemius. 8 These 

 facts are brought out in experiments in which the temperature of the muscle 



Stewart and Sollmann : L899, xxiv. p. 128. 



'Latimer: American Journal of Physiology, 1899, ii. p. 20. 



■> Philosophical Transactions <>/ the Royal Society <>/ London, 1899, Series B., v.. I. exci. p 363 



4 Gotschlich : Journal of Physiology, 1^'.)7, vol. xxi. p. 353. 



5 Ward, II. ( '. : Unpublished experiments at tin- University of Michigan. 



