The Influence of Environment 287 



We select for our discussion first the most influential 

 of external conditions, namely temperature. The 

 reader knows that there is a lower as well as an upper 

 temperature limit for life. Setchell has ascertained 

 that in hot springs whose temperature is 43° C, or 

 above, no animals or green algae are found.' In hot 

 springs whose temperature is above 43° he found 

 only the CyanophycecB, whose structure is more closely 

 related to that of the bacteria than to that of the algae, 

 inasmuch as they have neither definitely differentiated 

 nuclei nor chromophores. The highest temperature 

 at which Cyanophycece occurred was 63° C. Not all the 

 CyanophycecE were able to stand temperatures above 

 43° C, but only a few species. The other Cyanophycece 

 were found at a temperature below 40° C, and were no 

 more able to stand higher temperatures than the real 

 algae or animals. The Cyanophycece of the hot springs 

 were as a rule killed by a temperature of 73°. From 

 this we must conclude that they contain proteins whose 

 coagulation temperature lies above that of animals 

 and green plants, and may be as high as 73°. Among 

 the fungi many forms can resist a temperature above 

 43° or 45°; the spores can generally stand a higher 

 temperature than the vegetative organs. Duclaux 

 found that certain bacilli (Tyrothrix) found in cheese 

 are killed in one minute at a temperature of from 80° 



* Setchell, W. A., Science, 1903, xxvii., 934. 



