ALVEOLAR AIR. 115 



The higher tension of O 2 still remaining in the arterial blood 

 at the breaking point is not the only cause for the decidedly 

 longer time during which the breath can be held in the foregoing 

 experiment, another cause being that the CO 2 -combining power 

 of the blood will be less because it contains relatively more 

 oxy haemoglobin, than in the first experiment. Oxyhaemo- 

 globin is more acid than reduced haemoglobin. 



In both of the above experiments examine the gums and 

 the base of the finger nails for evidence of cyanosis (blueness) 

 and note the exact time at which it appears. 



The Effects of Forced Breathing. When the breathing 

 is made as deeply as possible, without materially altering the 

 rate, the alveoli become excessively ventilated with the result 

 that the CO 2 tension falls far below the normal level and free 

 CO 2 diffuses from the blood. The free CO 2 of the blood is 

 'washed out' or 'blown off' with the consequence that the acid- 

 base equilibrium of the blood changes, leaving a relative excess 

 of base. The condition of alkalosis hereby established causes 

 alteration in various physiological functions and the following 

 experiments are designed to demonstrate these. 



Experiment 49d. Have a person, while sitting, respire as deeply 

 as possible, at the normal rate, for ten minutes. During this 

 time count the pulse and measure the systolic blood pressure. 

 Examine also for evidence of cyanosis. After the forced breath- 

 ing, it will be found that for a time the person does not volun- 

 tarily breathe apnoea. Observe the thorax very carefully to 

 note the time at which the first indication of breathing returns. 

 Note the character of the first breath and of those which 

 succeed it. Make a diagram showing the character of the 

 breathing; also, count the pulse as frequently as possible and 

 look carefully for cyanosis. 



Experiment 49e. Measure the percentage of CO 2 in the alveolar 

 air of a person then instruct him to breathe deeply for ten 

 minutes (as in Experiment 43d), and during the last expiration 

 take another sample of alveolar air. Take a third sample at 

 the time the breathing just returns and a fourth one when the 

 normal breathing is reestablished (it will be advisable to have 

 at least two sampling syringes for these purposes). Chart the 



