§4] ACCLIMATIZATION TO EXTREME TEMPERATURES 255 



Since experiments have proved the fact of acclimatization, it 

 now remains to determine, if possible, its cause ; to ans\/er the 

 question, by virtue of what property can organisms whi-h, like 

 Flagellata, normally perish at 45° C. come to live at 70° or 

 even higher temperatures ? We have seen that death at high 

 temperatures is apparently due to coagulation of certain proteids 

 in the protoplasm which undergo a chemical change at between 

 45° and 50° C. Now, although the matter has not yet been 

 studied in these proteids, it has been shown for egg albumen 

 that in proportion as it is dried its coagulation point rises, as 

 the following table from Lbwith ('90) shows : — 



Since the coagulation point of egg albumen is raised by dry- 

 ness, it is very probable that a similar cause may act to raise 

 the coagulation point of protoplasm in organisms of hot springs. 

 Experimental studies are much needed upon this point. Mean- 

 while it can be said that one of the qualities which gives ca- 

 pacity of resistance to high temperatures is dryness. I shall now 

 cite some cases that I have collected, which prove this point. 

 It has been found that while moist yeast is killed at a tempera- 

 ture below 60°, dry yeast may be heated to 100° C. without 

 losing its vitality (SghIjtzenbekgbr, '79, p. 162). Damp 

 uredo-spores are killed at 68.5° to 60° C, but dry ones with- 

 stand up to 128° (Hoffman, '63); and dry spores of some 

 molds up to 120° (Pasteur, '61, p. 81). According to Dal- 

 LINGEE ('80, pp. 11-14), the dry spores of various Flagellata 

 are capable of withstanding a temperature from 10° to 27° 0. 

 higher than that which these spores can resist in fluid. Accord- 

 ing to DoYBRE ('42, p. 29), various animalcules (Rotifers, 

 Tardigrades) which cannot in water withstand a temperature 

 of 50° G. may, after long drying, be heated in air to 120° C. 



