340 RESPIRATION. 



respiration were within the limits of possibility. In accordance, 

 however, with his view of the quantity of carbonic acid contained 

 in the blood of the pulmonary capillaries, six respirations within 

 the minute would expel only 3'97^ of carbonic acid ; twelve would 

 yield 5'72-S; twenty-four 9'21 ; and forty-eight 16*1 8$. 



Although several causes, besides the frequency of respiration, 

 exert the most marked influence on the quantity of carbonic acid 

 in the expired air, this law nevertheless remains in force for other- 

 wise similar conditions, as Vierordt has convinced himself by 

 numerous series of experiments instituted under the most various 

 bodily conditions. We must, therefore, assume with him, that the 

 rhythm of the respiration acts as the most powerful regulator of 

 the excretion of carbonic acid. 



The influence of the respiratory movements on the excretion 

 of carbonic acid is equally manifested, when we consider the inten- 

 sity or depth of the individual respirations. Notwithstanding 

 the difficulty of drawing respirations of a certain depth, Vierordt 

 has been able to obtain very decisive results in relation to this 

 point, as may be seen in the following table : 



If the air of normal respirations contain 4'60 per cent, of carbonic acid, 



The air in respirations twice as deep contains 4'00 



three times 3' 70 



four times 3'38 



eight times 2'78 



half 5-38 



From these observations it follows, that in an expiration 

 having double the normal volume, the absolute quantity of the 

 exhaled carbonic acid is about equal to that which is exhaled by 

 respirations having threefold the normal frequency ; whence it is 

 further proved that the organism possesses two means of at the 

 same time separating larger quantities of carbonic acid. 



Vierordt adopted two methods of determining the question, 

 whether the amount of carbonic acid in the air increases in the 

 finer ramifications of the air-passages, as the experiments of Allen 

 and Pepys, and of Jurine, seem to show. One method consisted in 

 dividing each expiration into two as nearly as possible equal parts ; 

 the expired air in the latter half must have arisen from the deeper 

 parts of the lungs, and Vierordt found in it 5 -44-g- of carbonic acid 

 as the mean of 21 experiments, whilst the first half contained on 

 an average only 3' 72-g-. The other method consisted in comparing 

 the amount of carbonic acid in a normal expiration with that in 

 the air obtained by an intensely forced expiration. He found as the 



