LECTURE VI 



THE EFFECTS OF HEAT AND RADIANT ENERGY UPON LIVING 



MATTER 



i. EFFECTS OF HEAT 



IN discussing the effects of heat or temperature upon life phenom- 

 ena, we meet with the difficulty that heat influences living matter 

 in two ways; namely, chemically and physically. In chemical re- 

 gard the temperature influences the reaction velocity most powerfully, 

 and in physical regard it influences the viscosity of the liquids of the 

 cell (colloidal solutions) and their state of matter (coagulation, gela- 

 tion). In studying the influence of temperature upon life phenomena 

 we must keep these two effects apart. 



There is an upper temperature limit at which all organisms can be 

 killed; it is generally assumed that in this case death is due to the 

 fact that certain proteids are coagulated by heat, and this process is not 

 reversible. Setchell has ascertained that in hot springs whose tem- 

 perature is 43 C., or above, no animals or green algae are found.* 

 In hot springs whose temperature is above 43 he found only the 

 Cyanophycea, 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. are found at a temperature 

 below 40 C., and were no more able to stand higher temperatures than 

 the real algae or animals. The Cyanophycea of the hot springs were 

 as a rule killed by a temperature of 73. From this we must con- 

 clude that they contain proteids 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) 



* W. A. Setchell, Science, N. S., Vol. 27, p. 934, 1903. 



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