CHAPTER XI 

 TISSUES WHICH PRODUCE HEAT 



IN the last three chapters we have been studying tissues that were 

 differentiated and organized to produce three forms of energy for the use 

 of the organism. These were motion, electricity, and light. Protoplasm 

 also produces heat, and does it in the same way that it generates light and 

 electricity, by the secretion of substances that, when combined with 

 oxygen or some other reducing agent, generate the heat required. Where 

 known at all, the heat secretion appears in the form of granules which, 

 could they be specifically identified, might be called thermochondria. 



As the heat is produced by the oxidation of particles, it is probable 

 that when first generated it is concentrated into very small areas of the 

 cell. At this initial stage of liberation the concentrated heat must reach 

 what would appear to us as an enormous temperature. From these points 

 it rapidly radiates, to be distributed as lower and lower temperatures 

 to the various parts of the tissue and body. 



This heat is produced under two principal circumstances. First, 

 as a step in the process of generating motion or as a by-product in the other 

 physiological processes. This has been touched upon in discussing mo- 

 tion. Second, it is probably produced specifically and for the purpose 

 of maintaining a body temperature. 



The protoplasm of the animal body would not operate or live at the 

 absolute zero or at any temperature between that and the freezing point. 

 In most of the lower animals the required temperature is attained by 

 living in a climate whose air and water furnish the heat. The organisms 

 which live and are active in Arctic seas and on the sea bottom at great 

 depths exist normally in a temperature that is but little above the freez- 

 ing point. Others require more heat, and while they will not die for a 

 while at or somewhat below the freezing point, they cannot live per- 

 manently unless in a temperature considerably above this. Therefore 

 they seek a warmer climate or the rays of the sun on a rock at noonday. 

 Countless forms, especially such as insects and reptiles, live through the 

 cold of winter or of the tropic night, in the high altitudes, and only come 

 out and are active during the summer time or the heat of midday. 



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