EXTERNAL INFLUENCES AS CAUSES OF VARIATION 261 



Death from low temperatures appears to result from entirely 

 different causes. Protoplasm seems to contain no substance but 

 water that undergoes either chemical or serious physical change 

 by low temperatures. Many yeast cells endure 1 13.7 C. 

 (Schumacher). 



De Candolle subjected " various dry seeds and spores of bac- 

 teria to a temperature of nearly 200, at which temperature the 

 atmosphere becomes liquefied, but without fatal effects." " Cilia 

 from the mouth of the frog were cooled to 90, and recovered 

 their movement upon raising the temperature." " Eggs of the 

 frog, lowered slowly to 60, can revive." From facts such as 

 these Davenport concludes that "there is no fatal temperature 

 for dry protoplasm." * 



The first effect of lowering temperature is a slowing of activity, 

 followed, finally, by complete cessation. As is pertinently re- 

 marked by the author just quoted, " The fact that cold rigor 

 usually occurs close to the zero point (C.) indicates that the 

 activities of protoplasms are closely determined by the fluid 

 state of water," and " the critical point for vital activity has 

 been adjusted to this critical point of water." 2 



There is much lack of information upon the exact cause of 

 death from excessive cold. Among the higher animals the 

 immediate cause is without doubt asphyxia from the cessation 

 of the blood flow ; but among the simpler organisms the matter 

 is not so clear. What evidence we have seems to indicate that 

 the primary cause of death is in all probability the mechanical 

 rupture of protoplasm and cell wall by freezing water expanding 

 as it solidifies. 



In any event experience and experiment agree in indicating 

 that protoplasm is resistant to" excessive cold in the absence of 

 moisture, and in all study of this matter we are to remember 

 two facts : first, that the freezing point of all protoplasm is 

 lower than that of water only ; and, second, that as long as the 

 slightest activity is present heat is being produced. From these 

 two facts the protoplasm is able to resist actual solidifying much 



1 C. B. Davenport, Experimental Morphology, Part I, pp. 240-242. Though 

 not so stated in the text quoted these temperatures are C. 



2 Ibid. p. 242. 



