350 THE RESPIRATION 



velops more rapidly than in the large cabinet, and a higher percentage 

 (10 per cent) of C0 2 can be tolerated. That in this case also deficiency of 

 2 is not responsible for the hyperpnea can be shown by repetition of the 

 experiment either with an excess of 2 in the bag or with absorption of the 

 C0 2 by soda lime. In the former case hyperpnea will develop as usual, 

 while in the latter it will not supervene until the percentage of 2 has 

 fallen below 10, when cyanosis becomes marked. In fact, some people 

 become cyanosed and unconscious, and collapse under these conditions 

 before there is any respiratory disturbance. A peculiarity of the effect 

 of 2 deficiency is that the person may be unaware of the seriousness 

 of his condition ; indeed he may be somewhat stimulated. The conclusion 

 may be drawn that deficiency of 2 per se can serve as a respiratory 

 stimulus only when it is so extreme as to cause other serious symptoms. 

 This conclusion does not rule out an important influence of 2 deficiency 

 in increasing the excitability of the center towards C0 2 . Under ordi- 

 nary conditions, however, the center is far more sensitive towards slight 

 changes in the C0 2 percentage. 



There is an obvious reason why the adjustment of pulmonic ventila- 

 tion should not depend upon changes in 2 supply to the respiratory cen- 

 ter. If.it were so, many other tissue activities and other nerve centers 

 would suffer from the 2 deficiency before there was time for the breath- 

 ing to become stimulated sufficiently to make good the loss of 2 . As a 

 matter of fact, headache, dizziness, nausea and even fainting are almost 

 certain to be caused whenever any muscular exercise is attempted in an 

 atmosphere containing a deficiency of 2 but no excess of C0 2 (cf. moun- 

 tain sickness). An adequate 2 supply of the body is, therefore, insured 

 by changes in C0 2 tension of the blood. 



Quantitative Relationship between C0 2 of Inspired Air and Pulmonary 

 Ventilation. These results suggest, as the next step in the investigation 

 of our problem, the determination of the quantitative relationship be- 

 tween the C0 2 percentage of the respired air and the amount of air 

 breathed (pulmonic ventilation).** That there is such a relationship has 

 been most successfully demonstrated by R. W. Scott, who used for his 

 purpose decerebrate cats.f The trachea was connected, through a T-tube 

 provided with valves, with tubing leading to a large bottle and a Gad-Krogh 

 spirometer, so that the animal breathed out of the bottle into the 

 spirometer, these two being also connected together. The spirom- 



*A distinction is somewhere drawn between pulmonic ventilation and alveolar ventilation, the 

 former being the total amount of air that enters and leaves the lungs, and the latter, that which en- 

 ters and leaves the alveoli. This distinction is based on the 'assumption that the capacity of the dead 

 space may vary considerably from time to time, which, as pointed out elsewhere, is erroneous. For 

 practical purposes pulmonic ventilation is the safer value to give. 



fDecerebrate animals must be used in these experiments, since anesthetics markedly depress the 

 activity of the respiratory center. 



