§3] TEMPERATURE-LIMITS OF LIFE 239 



agulates at the death point of organisms? As KtJHNE ('64, 

 p. 1) pointed out, it cannot be ordinary egg albumen ; for, 

 excepting the contractile substance, we know of no native 

 albumen which coagulates between 35° and 50° C. It was 

 Kuhnb's great service to. show that there is a substance which 

 can be pressed out of frozen, triturated, and then thawed 

 muscle, which becomes quickly opalescent at 40°, through the 

 separation of the muscle plasma into myosin and a serum. 

 This serum, in turn, contains an albuminoid which coagulates 

 at 47° (Demant, '79 and '80). Now, since there are proteids 

 in muscle which coagulate at about the point at which muscle 

 goes into permanent heat-rigor, and since these proteids can 

 no longer be squeezed out of rigid muscles, the conclusion 

 seems justified that permanent heat-rigor in muscle is due to 

 the coagulation of these proteids. 



Related, easily coagulable proteids occur in widely dissimilar 

 organisms. For example, myosin has been found in vegetable 

 protoplasm (Wbyl, '77, p. 96), and Halliburton ('88) has 

 described a globulin from blood corpuscles which coagulates 

 at 48° to 50°. Their distribution in protoplasm is, therefore, 

 probably general, and so we are justified in concluding that the 

 death of protoplasm by heat is, in general, the result of the 

 coagulation of a proteid (globulin). Death occurs because 

 the vital machinery has been broken down.* 



2. Temporary Rigor and Death at the Lower Limit of Tem- 

 perature, Minimum and Ultraminimum. — Whilst towards the 

 upper limit of ordinary terrestrial temperatures (35° to 40° C.) 

 molecular changes in organic compounds are hastened, towards 

 the lower limits (— 40° to — 50°) molecular changes are slow, 

 being principally confined to the transformation from the liquid 

 or gaseous to the solid or liquid condition. This transforma- 

 tion does occur in the water of protoplasm, but the colloids, 



* At this place reference may be made to the fact that protoplasm subjected 

 to a high temperature sometimes breaks to pieces with the suddenness and com- 

 pleteness of an explosion. Thus Strasburger ('78, p. 611) found that Chilo- 

 monas ourvata was uniformly killed at 45° C. by the explosion of the body, and 

 Dr. W. E. Castle tells me that he has observed the same phenomenon under 

 like conditions in Stentor. An investigation of this profound change in pro- 

 toplasm would be sure to throw valuable light upon the nature of the living 

 ■substance. 



