RESPIRATION 121 



connected to the lower end of the gas burette. After all the air has 

 been expelled from the connections, turn the three-way stopcock in 

 such a position as to permit the pyrogallate to flow up into the gas 

 burette, coming in contact with the air to be analyzed. The pressure 

 tube should now be elevated as high as the connecting rubber will 

 permit and the potassium pyrogallate solution allowed to run into 

 the burette A. The clamp on the connecting tube should now be 

 applied to it close to the lower end of the burette. 



This operation made positive pressure in the burette, thereby 

 causing a more rapid absorption of the oxygen. The burette should 

 now be taken by the experimenter and its ends alternately raised 

 and lowered. At frequent intervals he should loosen the clamp on 

 the connecting rubber tube and raise the pressure tube, thus permit- 

 ting potassium pyrogallate solution to take the place of the oxygen 

 as it is absorbed. This procedure should continue ten minutes, after 

 which the clamp on the connecting rubber tube should be loosened. 

 The burette and its pressure tube should be allowed to remain ten 

 minutes longer, at the end of which time the solution in the burette 

 should be brought to a level with the solution in the pressure tube 

 by elevating or lowering the tube. This causes the air in the burette 

 to be under the atmospheric pressure existing at that time. The 

 reading for the amount of oxygen is now taken. 



To calculate the amount of oxygen consumed by the animal, one 

 subtracts the amount of oxygen found in the respired air from that 

 found in the normal air. At least one sample should be analyzed 

 from each 10 litres of respired air, the average being used to obtain 

 the result. 



VIII. THE RESPIRATORY QUOTIENT. 



The respiratory quotient being the ratio between the volume of car- 

 bon dioxide exhaled and that of oxygen consumed (R.Q. = 2 j , 



it may be'computed from data given in Exercises VI. and VII., or it 

 may be directly determined in the following manner: 



1. Appliances. Ventilating apparatus (Fig. 64); animal cage; 

 CaCl 2 tube; Geissler bulbs ; two barium hydrate flasks; 25 percent, 

 solution of KOH; 5 per cent, solution of pyrogallic acid; two gas 

 burettes with pressure tubes; guinea-pig or small rabbit. 



2. Preparation. Pass one end of the glass tube out through hole 

 in window sash; to inner end attach a rubber tube to whose other 

 end is joined a Ba(OH) 2 flask, followed by cage, CaCl 2 tube, Geissler 

 bulbs, barium flask, and ventilating apparatus, as shown in the 

 figure. Weigh animal cage. Note temperature of room. 



3. Operation. Put the animal into the cage; take weight. Start 

 the ventilation, noting the time. While the first pressure bottle is 



