480 Historical 



partial pressure also increases the proportion of oxygen in simple 

 solution in the blood, whereas that which is in a state of chemical 

 combination there very probably does not vary. This shows that it is 

 not the oxygen simply dissolved, but the oxygen combined which pro- 

 duces the carbonic acid, since in the experiments of Regnault this 

 production did not increase. 



We can see likewise that the increase of oxidation and of carbonic 

 acid production which we observed in compressed air is caused by 

 the combined oxygen of the blood. (P. 147.) 



Passing to another class of phenomena, the Danish physiologist 

 studies the changes in the respiratory rhythm. We have quoted 

 in the preceding chapter the data which he obtained. To explain 

 the increase of the pulmonary capacity, he makes the following 

 experiment: 



I immerse under water in a flask a bladder half full of air; a 

 second bladder provided with a tube is placed upon the first; the tube 

 passes through a stopper which hermetically closes the flask, which 

 therefore is full of water except for the space occupied by the bladders. 

 The lower bladder represents the intestinal tube and its gases, the 

 upper one represents the lungs with the trachea, the flask and the 

 water representing the closed thoracic cavity. If this very simple 

 apparatus is carried into compressed air, we see that the lower bladder 

 decreases while the upper one increases in volume. 



This result is not at all changed if we use a flask the bottom of 

 which is replaced by an elastic membrane. The closed bladder behaves 

 in the same way; but only a part of the space which it leaves free is 

 filled by the upper bladder; the membrane at the bottom rises. 



This shows that it is the compression of the air contained in the 

 intestine which is the cause of the increase in the lung capacity and 

 the greater lowering of the diaphragm. 



The changes in the respiratory rhythm could not be explained, 

 Panum says, by the increase in the oxygen of the blood, since this 

 increase leads to apnea; now in apnea, not only the number but 

 also the amplitude of the respiratory movements decrease. He 

 also rejects the hypothesis accepted by Vivenot and G. Lange of 

 an increase in the power of the inspirator muscles; he justly con- 

 siders that these authors gave no proof of their assertion. In his 

 opinion, it is the increase in the average capacity of the lungs, 

 under the direct, mechanical influence of compressed air, which 

 causes the deeper inspirations. 



In regard to the changes in the pulse and the increase of the 

 arterial pressure, Panum finds quite contrary to the laws of physics 

 ("ganz unphysikalisch") the explanation of Vivenot, G. Lange, 

 Sandahl and Elsasser, which attributes them to an alleged decrease 



