240 HEAT AND PROTOPLASM [Ch-VIH 



which constitute the living part, are not modified by even the 

 lowest of the terrestrial temperatures, except that the molecular 

 changes which they undergo are very slow. This being true, 

 protoplasm which contains no water, or very little, ought not to 

 be changed by low temperatures, — that is to say, the machine 

 will not be injured. 



With the activities of the machine — with the vital processes 

 — it is, however, quite different. They are essentially chemical 

 ])rocesses, and hence we should expect them to be diminished 

 at a low temperature. If, as Pictet ('93) maintains from an 

 extensive and highly important series of experiments, no chemi- 

 cal processes take place at temperatures below — 100° C, then 

 protoplasm ought to exhibit no vital processes at this tempera- 

 ture, and, indeed, experience shows that, as we have already 

 seen, as the temperature is lowered below the optimum, all 

 manifestations of activity diminish. It is clear that at a certain 

 point they must entirely cease. And at that point death, 

 following the usual definition of the word, would ensue. 



But does the cessation of the vital processes, without injury 

 to the mechanism, necessarily preclude the possibility of a 

 return to activity ? Let us examine the experimental .evidence 

 on this point. Schumacher ('74, p. 179) subjected yeast to 

 cold and found that, at the lowest temperature produced 

 (— 113.7°), the yeast cells were not completely killed. More 

 recently, PiCTET ('93% cf. also C. de Candolle, '84) has sub- 

 mitted various dry seeds and spores of bacteria to a temperature 

 of nearly — 200°, at which temperature the atmosphere becomes 

 liquefied, but without fatal effects. Other results were still 

 more remarkable : vibratile cilia from the mouth of the frog 

 were cooled to — 90°, and recovered their movement upon 

 raising the temperature. Some Rotifera and Infusoria were 

 frozen in their native water at — 60°, and kept at that tem- 

 perature, apparently, for nearly 24 hours. Most have subse- 

 quently regained their activity. Eggs of the frog, lowered 

 slowly to — 60°, can revive. Eggs of the silk-worm can resist 

 to —40°. Other experiments of Pictet* will be referred to 



* This general criticism of Pictet's paper is, I believe, valid. He does not 

 give us data enough upon time of subjection to the low temperature, time em- 

 ployed in reducing the temperature, and other details. Thus, concerning his 



