336 RESPIRATION. 



The above remarks indicate that the frequency or depth of 

 the respiratory movements must exert considerable influence on 

 the interchange of gases in the lungs. Before we proceed to the 

 other relations by which the pulmonary functions are modified, 

 we will consider these purely mechanical relations somewhat more 

 attentively, especially since many other physical and physiological 

 influences affect the respiratory functions, and particularly the 

 excretion of carbonic acid, only in an indirect manner by modify- 

 ing the respiratory movements. Notwithstanding the attention 

 which has been directed to the mechanism of respiration in its 

 anatomical and physiological relations, and the number and 

 excellence of the investigations made in reference to the chemical 

 constitution of the expired air and the differences which it 

 presents under the most different physiological conditions, this 

 most important factor in the process of respiration remained 

 almost entirely unnoticed until Vierordt published his well-known 

 work on the subject, which he has so thoroughly exhausted that 

 all our knowledge of the relations in question may in fact be 

 referred to him alone. We cannot, therefore, do better than follow 

 him as our guide in these inquiries. 



Vierordt first limited his investigations solely to the determi- 

 nation of the dependence of the amount of carbonic acicl in the 

 expired air upon the frequency of the respiratory movements ; to 

 ascertain this relation, he began by observing the quantities of 

 carbonic acid excreted during perfectly quiet respiration, in order 

 to obtain certain mean values and to establish the corresponding 

 variations. All Vierordt's experiments were made upon himself, 

 and, as nearly as possible, under the same conditions. The 

 duration of each experiment was limited to a minute, and the air 

 collected during that period was tested for its amount of carbonic 

 acid. Before each experiment a few respirations were made, cor- 

 responding in frequency as nearly as possible to those made 

 during the period of the experiment, since the air remaining in the 

 lungs from the previous respirations might have induced a relative 

 error in the result of the observation. These comparative observa- 

 tions on the different frequency of the respiration were not made 

 consecutively, but at intervals of about half an hour, and, as far as 

 possible, at the same time of the day. The volumes of gases given 

 in the following table are calculated for a temperature of 37, and 

 the barometer at 336 Paris lines. 



Vierordt found the following mean values, to which we add the 



