238 HEAT AND PROTOPLASM [Cii. VTII 



experiments were carried on is supposed to be, except for its 

 temperature, normal for tlie species. Summarizing the table, 

 we find that the Protista have the highest maximum tempera- 

 ture of any group, it being in extreme cases about 60° for active 

 organisms, but generally between 40° and 45°. Among the 

 Metazoa, the highest maxima recorded (excepting Rotifera and 

 Tardigrada) are 44° to 45° for Turbellaria, Anguillula, Naididse, 

 Nepa (water-scorpion), Notonecta (water-boatman), Cloe larva, 

 Salamander, and mammals. A water-mite (Hydrachna) is 

 said to have withstood up to 46.2°, and some vertebrate tissues 

 resist up to 50°. For the great majority of Metazoa, the maxi- 

 mum temperature lies below 45° and, in the case of marine 

 species, below 40°. The low maximum temperature of marine 

 species is probably due to the low maximum temperature of 

 the sea as compared with ponds. We may consequently con- 

 clude from the foregoing that the maximum temperature for 

 protoplasm lies generally between 35° and 50°, the lower limit 

 being characteristic of organisms living in a medium of low 

 temperature (the sea), the latter, of organisms reared in warm 

 pools or of organs (vertebrate muscle) in a body kept at a high 

 temperature. 



The question now arises, what is the cause of the death of 

 protoplasm at high temperatures? To get some insight into 

 this matter, let us examine the phenomena accompanying death 

 of protoplasm from overheating. Kuhne ('64, p. 44) thus 

 describes the appearance of an Amoeba subjected for a moment 

 to a fatal temperature (45°). The structure is entirely altered 

 since it has become transformed into a mass of knobbed, opal- 

 escent, solid lumps, which, even in transferring to the slide, 

 become easily broken apart. This appearance is clearly due 

 to a coagulation of the protoplasm. A similar coagulation 

 takes place in Actinophrys eichhornii (Kuhne, '64, p. 67) at 

 45°. "' The sphere shrinks into a flat, hardly transparent, cake, 

 no longer reacts to the strongest induction shocks, and breaks 

 up after 24 hours into a heap of small granules and irregular 

 pieces." Likewise, in muscles a change is produced by heat 

 which is evidently a kind of coagulation. A coagulation then 

 seems to be the immediate cause of death at high temperatures. 



But just what is the component of protoplasm which co- 



