3] TEMPERATURE-LIMITS OF LIFE 238 



lengthening again as the temperature falls. If, however (GoT- 

 SCHLICH), the temperature is raised in about 60 seconds to 38 

 and then lowered, the elongation of the muscle takes place only 

 very slowly. This is the condition of u thermische Dauerverk- 

 urzung," and is probably the same as the condition of tempo- 

 rary heat-rigor of SACHS. When, however, the temperature 

 is raised rapidly to 45 to 50 (or slowly to 35), death-rigor 

 appears, accompanied by a coagulation of the protoplasm 

 which renders the whole mass opaque and permanently con- 

 tracted. The rapidly replaced contraction accompanying ele- 

 vation to about 30, the slowly obliterated contraction of 38, 

 and the permanent contraction of 45 are then three stages in 

 a series of effects of heat on muscle. 



If now, contraction, heat-rigor, and death-rigor are merely 

 three stages in a series of effects of increasing temperature, 

 they probably have related immediate causes. Heat-rigor is 

 certainly a condition of tetanus, but the fact that the proto- 

 plasm in this condition is not sensitive and cannot quickly 

 return to the relaxed condition indicates that some of those 

 changes that produce death-rigor have already occurred, but 

 not to such an extent that the organism cannot recover from 

 them. As GOTSCHLICH says ('93, p. 154), "Die thermische 

 Dauerverkurzung ist also eine qualitative unvollendete Starre" 

 (i.e. death-rigor). From this point of view there is no exact 

 point at which heat-rigor occurs, since the period of persisting 

 rigidity varies in extent from to many hours, and thus passes 

 by almost imperceptible gradations from a contraction in re- 

 sponse to heat on the one hand to death-rigor on the other. 

 The muscle increases in sensitiveness as the temperature rises 

 to the optimum, just as the movements of plasma in Chara do. 

 Beyond the optimum, sensitiveness diminishes, and this leads 

 to a condition of heat-rigor which becomes the more pronounced 

 the higher the temperature, until, through completed coagula- 

 tion, death occurs. 



We must now consider this point at which death occurs 

 from heat ; and, as an introduction to this discussion, we 

 may tabulate the results of experiments by numerous ob- 

 servers who have attempted to determine the ultramaximum 

 temperature. 



