§3] TEMPERATURE-LIMITS OF LIFE 243 



of water, those chemical changes rapidly occur which we desig- 

 nate response to the stimulus of cold. This composition of 

 protoplasm, upon which cold can work such important modifi- 

 cations, is a quality of immense importance in the economy of 

 the organism, as the changes of each autumn testify. 



Below the point of temporary cold-rigor lies that of death, 

 if death point there be. The position of the death point is, 

 however, very diverse in different organisms. Part of the 

 diversity in the death points assigned by different authors is, 

 however, due to the fact that in the methods of determining 

 the death points there has been a lack of uniformity. 



Five elements ought always to be regarded in experiments 

 on the ultraminimum temperature. (1) History of the tem- 

 perature conditions in which the individual or its race had 

 lived before experimentation ; (2) rate at which the organ- 

 ism has been cooled, — if possible, the temperature of the 

 organism itself rather than that of the medium ; (3) inten- 

 sity of cold just sufficient to kill; (4) duration of applica- 

 tion of the cold and the kind of medium in which the 

 organism is subjected to the cold ; * and (5) the rate of 

 thawing out.f These elements have been too much neg- 

 lected in the past. 



I shall now present in tabular form some of the more 

 reliable determinations of the death point of organisms, pref- 

 acing with the caution that the results are not closely 

 comparable. 



* The duration of application and intensity of tlie fatal cold stand in an 

 inverse relation, so that organisms which resist a temperature — ^° for X min- 

 utes will resist a lower temperature, —{A + a)°, for a shorter time, X — x. 

 Thus, Clepsine complana resists — 8°C. for 15 minutes ; — 5°C. for 90 minutes. 

 So Planorbis corneus resists — 7° for 5 hours, but — 5° for 48 hours. Again, 

 Musca domestioa can resist — 12" for 5 minutes ; — 8° for 20 minutes ; and 



— 5°C. for 40 minutes. (Roedel, '86.) Since many authors have little re- 

 garded the duration of action of the cold, their determinations have little 

 scientific value. 



t The importance of this is illustrated by some experiments of Sachs 

 ('60, p. 177), who found that the leaves of the beet or cabbage frozen at from 



— 4° to — 6° died if they were thawed in air at 2° or 3°, or in water at 6° to 

 10° ; but lived when slowly thawed in water at 0°. In general, the more gradual 

 the thawing, the lower the fatal temperature; 



