[camerox-brownlee] low TEMPERATURES ON THE FROG 115 



death of the protoplasm is directh' due to withdrawal of water through 

 ice-separation. Recently however Apelt* has shown, in experiments 

 with the Potato, that the freezing-point of the cell-sap is always higher 

 than the death-point of the cell. Voigtlanderf finds as the result of 

 numerous experiments that many species can be supercooled far below 

 the specific death-temperature. Ice must be formed in the tissues 

 before death takes place, but the formation of ice is in itself insufficient. 

 Death takes place only when the temperature falls below a certain 

 minimum, specific for each species, and which can in certain cases lie far 

 below the eutectic point of the salt mixture in the cell-sap. His results 

 therefore do not agree with the MuUer-Thurgau hypothesis, and he is 

 of the opinion that the actual cause of death is not yet known. It is 

 at any rate evident that the phenomena described bear many resem- 

 blances to those exhibited by the cooled frog. 



Jensen and Fisher | have attempted, by studying the slight dif- 

 ference of curvature by plotting temperature against time (as in figure 

 1) for frog's muscle and 0'7 per cent sodium chloride solution gradually 

 cooled, to determine the relative amounts of "free" water and water 

 absorbed in the colloid of the muscle. They conclude that the latter 

 amounts to only a few percentage of the whole amount, from which 

 it would appear that considerable variations of concentration of the 

 cell-fluid may be possible without damage to the cell-protoplasm. 



Our experimental results are in sulDstantial agreement with Gadow's 

 views (p. 109) and appear to show conclusively that the frogs experimented 

 on^ — R. pipiens from the neighbourhood of Ciiicago — will not survive 

 a temperature of -1'8°C. It would therefore appear highly probable 

 that the Manitoban frog, although it has to survive a severer winter, 

 survives only when it is not subjected to a temperature of -1'8°C. 

 Two possibilities are conceivable under which exposure to a lower 

 temperature would not be fatal. The first is that, for frogs at a depth 

 of several feet of earth the rate of freezing might be so gradual as to 

 introduce some compensating factor, some new phenomenon. The 

 apparently definite death-temperature of the various tissues does not 

 appear to warrant this assumption nor can any physical chemical 

 process be advanced in support of it. The second supposition is that 

 there is a fundamental difference between the Manitoban and Illinois 



*"Neue Untersuchungen iiber den Kaltetod der Kartotieln," Beitr. zur Biol, 

 der Pflanzen, 9, 215, Zentr. f. Physiol., 22, 538, 1908. 



t "Unterkiihlung und Kaltetod der Pflanzen," Beitr. zur Biol, der Pflanzen, 9, 

 359, 1910; Zentr. f. Physiol., 24, 271, 1910. Compare also Rein (Untersuchungen 

 tiber den Kaltetod der Pflanzen," Zeit. f. Naturwiss., 80, 1; Zentr. f. Physiol., 23, 

 85) who concludes that the death-temperature is completely independent of the 

 osmotic pressure in the cell. 



J"Die Bindung des Wassers im Muskel," Zentr. f. Physiol., 23, 296, 1909. 



