THE THYROID 37 



have given much attention to the study of "respira- 

 tory exchange" to the relationship of oxygen in- 

 take and carbon dioxide output, and to the meas- 

 urement of the heat evolved in the reaction. Vari- 

 ous types of calorimeters have been invented for 

 that purpose. 1 In Germany, Voit, Pettenkofer, 

 Kubner and Zuntz, and in this country, Atwater,- 

 Eosa and Benedict, have done much to advance our 

 knowledge in this direction. The sum of such 

 knowledge has been to supply us with exact data 

 regarding the heat evolved in individuals under 

 varying conditions. If a certain amount of heat 

 is evolved, that amount of heat must also be sup- 

 plied, and the supply of such heat can come only 

 from the food supplied and "burnt" in the body. 

 That is how we arrive at certain fundamental food 

 requirements. 



Constant Temperature. Not the least remark- 

 able of the many remarkable phenomena noticeable 

 when we study the living organism is the way the 

 temperature within us remains constant. The 

 temperature outside may vary considerably, yet 

 under normal conditions the temperature within 

 us varies very little. A constant temperature 

 means a constant heat production. 



Of course this is true only of warm-blooded ani- 

 mals, not of cold-blooded ones, such as the frog; 



1 See the chapter on Calories in the author's book on Vitamines. 



