ELEMENTARY DEMONSTRATIONS 145 



70 kilos, the mean daily output of C0 2 equals 800 grms., and the mean 

 intake of 2 equals 700 grms. A half-metre cube roughly represents 

 the volume of the intake of 2 or output of C0 2 . Note the size of this 

 cube. In rest, walking three miles an hour, and on the tread-mill the 

 production of C0 2 is roughly in the proportion 2, 3, and 6. 



The warm-blooded animal responds to a rise or fall in external 

 temperature with a decrease and increase respectively of C0 2 output. The 

 normal response occurs only so long as the body temperature is normal. 

 A man deeply anaesthetised, or one in whom the spinal cord in the 

 upper dorsal region has been divided, or a new born babe, responds 

 (like a cold-blooded animal) to a fall of external temperature by 

 diminished metabolism and fall of body temperature. The surface 

 area of the body, in proportion to the mass, is much greater in the 

 child than in the adult, and in the tall, thin man, than in short, fat man. 

 The respiratory exchange is therefore greater in the child and the tall 

 thin man. 



r*o 



The respiratory quotient -^ indicates the amount of oxygen used 



in the oxidation of carbon. On a carbohydrate diet the R.Q. is 1 for 

 C 6 H 12 6 + 60 2 = 6C0 2 + 6H 2 0, and by Avogadro's principle a mole- 

 cule of 2 occupies the same volume as a molecule of C0 2 . The R.Q. 

 is less than 1 on a fat or proteid diet, for a certain amount of 2 is used 

 up in the oxidation of H 2 and of the nitrogenous elements of the food. 



In the case of a fat diet (olein) the final stage of the metabolic process 

 has been represented thus : 



C 3 H 5 (C 18 H 33 2 ) 3 + 800 2 = 57C0 2 + 52H 2 0, and the R.Q. is |J = 071. 

 On an ordinary mixed diet R.Q. = O'S, while on a strict diabetic diet it 

 may fall to 0'6. On the latter diet the 2 intake may be almost 

 doubled. When an animal is rapidly putting on fat the R.Q. may 

 become greater than 1, for the C0 2 output is increased owing to the 

 conversion of carbohydrate into fat ; it appears that, in addition to the 

 ordinary combustion which results in a quotient approaching unity, 

 there is a discharge of a further quantity of carbon dioxide, the oxygen 

 of which is derived from the intramolecular oxygen of the food. 



CHAPTER XL. 

 RESPIRATION APPARATUS. 



The Haldane-Pembrey Respiration Apparatus fo* the Mouse. The 



apparatus is constructed as in Fig. 128. The corks are soaked in 

 melted paraffin before insertion. Each double absorption tube is fitted 



K 



