330 



RESPIRATION 



at room temperature and pressure. Wash the sample back and forth 

 through the potash bulb as directed ten times and read for absorption of 

 the carbon dioxide. Next wash in ten per cent, pyrogallic acid in potas- 

 sium hydroxide until constant readings show that all oxygen is absorbed. 



FIG. 246a. Apparatus for Demonstrating Excess of CO 2 in Expired Air. Flasks filled 



with lime-water. 



The nitrogen residue is calculated by difference. Compute the per- 

 centages of carbon dioxide, oxygen and nitrogen. 



Expired Air. Exhale ten expirations controlled by one-way valves 

 into an ordinary respirometer or a Tissot apparatus. Now fill the Guthrie 

 apparatus with a sample of this expired air and analyze as before, first for 



FIG. 2466. Change in Respiration on Stimulating the Central End of the Sciatic 

 Nerve. The rate is sharply increased and the amplitude more than doubled. The 

 stimulation is between the points marked on and off, time in seconds. The inspiratory 

 movement following the stimulation was greater than the limit of the recording tambour. 



carbon dioxide, then for oxygen; compute the percentage of each gas, 

 including nitrogen. The expired air will usually be found to have lost 

 from 4 to 5 per cent, of oxygen and have gained a little more than that 

 quantity of carbon dioxide. 



