426 RESPIRATION. 



one experiments, a percentage of 3 '72 in the first part of the 

 expiration, and 5*44 in the second part. 1 



Temporary arrest of the respiratory movements, as we 

 should expect, has a marked influence in increasing the pro- 

 portion of carbonic acid in the expired air ; though the abso- 

 lute quantity exhaled in a given time is diminished. In a 

 number of experiments on his own person, Yierordt ascer- 

 tained that the percentage of carbonic acid becomes uniform 

 in all parts of the respiratory organs, after holding the 

 breath for 40 seconds. Holding the breath after an ordinary 

 inspiration for 20 seconds, the percentage of carbonic acid 

 in the expired air was increased 1*73 over the normal stand- 

 ard ; but the absolute quantity exhaled was diminished by 

 2*642 cubic inches. After taking the deepest possible inspi- 

 ration, and holding the breath for 100 seconds, the percent- 

 age was increased 3*08 above the normal standard ; but the 

 absolute quantity was diminished more than 14 cubic inches. 2 

 Allen and Pepys state that air which has passed 9 or 10 times 

 through the lungs contains 9*5 per cent, of carbonic acid. 3 



Yierordt gives the following formula as representing the 

 influence of the frequency of the respirations on the produc- 

 tion of carbonic acid : Taking 2'5 parts per hundred as rep- 

 resenting the constant value of the gas exhaled by the blood, 

 the increase over this proportion in the expired air is in 

 exact ratio to the duration in the contact of the air and 

 blood. This, though it may hold good in many instances, 

 seems rather an excessive refinement. 4 



1 LEHMANN, Physiological Chemistry, Philadelphia, 1855, vol. ii., p. 439. 

 ' 2 Cyclopaedia of Anatomy and Physiology, vol. iv., part 1, p. 352. 



3 Ibid. 



4 The following table gives at a glance the most important results of these 

 experiments : 



Proportion of Carbonic Acid. Number of Respirations per Minute. 



5-7 per 100 parts of air C 



4-1 " " " 12 



3-3 " " " 24 



2-9 ' " " 4S 



2-7 - H " % 



