320 A TEXTBOOK OF PHYSIOLOGY 



With carbohydrate the quotient is 1. The following formula 

 summarizes its decomposition: 



C 6 H 10 O f) + 60 2 P. 6C0 2 + 6H 2 0. 



6ca_ 1 



60 2 "" 



In the case of carbohydrate there is sufficient oxygen in the mole- 

 cule for the formation of water ; oxygen is only required for the forma- 

 tion of carbon dioxide. In the case of protein and fat part of the 

 oxygen taken in combines with hydrogen to form water; the R.Q. 

 is therefore less than 1. With protein it is about 0-82. The following 

 formula has been suggested as summarizing its decomposition : 



C 72 H 112 N 18 22 S + 770 2 = 63C0 2 + 38H 2 O + 9CO(NH 2 ) 2 + SO ;J . 



Urea 



C0 2 63 _ 2 

 OT = 77~ 



For fats undergoing direct katabolism in the body it is found to 

 be about 0-7. The following formula summarizes the katabolism of 

 olein : 



C 3 H 5 (C 18 H 33 2 ) 3 4- 800 2 = 57C0 2 + 52H 2 O. 

 CO 2 _ 57 rv. 71 

 O t "80 ; 



Muscular work, although greatly increasing the respiratory ex- 

 change, may not affect the respiratory quotient. The respiratory 

 quotient of animals previous to and during hibernation and during 

 starvation is referred to under Fat Metabolism (pp. 439, 440). 



Internal or Tissue Respiration denotes gaseous interchange between 

 the blood and tissue fluids on the one hand, and the body cells on 

 the others. A frog placed in nitrogen continues to produce C0 2 for 

 some hours, so does a frog whose blood is replaced by physiological 

 saline. Excised " surviving " organs, artificially circulated, continue to 

 use 2 and produce C0 2 . The glow organ of a glow-worm glows only 

 in the presence of oxygen. These^ are proofs of tissue respiration. 

 That the livingfctissues have a marked affinity for oxygen can be 

 shown by injecting a solution of methylene blue intravenously. On 

 killing the animal, it is found that, although the blood be blue, the 

 tissues, such as the muscles, are uncoloured. Upon exposing the 

 muscles to oxygen, they become blue, showing that the muscles have 

 reduced the methylene blue, and thus decolorized it. Since methylene 

 blue is a fairly stable compound, the great affinity of the tissues is 

 well shown by the experiment. They store up but little combined 

 oxygen, and the oxidative changes which occur in them are supposed 

 to be due to enzymes known as " oxidases " and " peroxidases " 

 (see p. 73)- When a tissue is active, much more oxygen is taken 

 from the circulating blood and mo^e C0 2 is given up to the bloocl. 

 This gaseous interchange can be calculated by estimating the amount 

 of C0 2 and O^n the blood going to and leaving the organ, and by 



