388 



PHYSIOLOGY 



CHAP. 



In order to determine the tension or partial pressure of the O 2 or CO 2 of 

 the air (at 0., and mean pressure of 760 mm. Hg) it is sufficient to know 



FIG. 170. Pfliiger's pulmonary catheter, modified by Ludwig. 



its percentage composition. Since inspired air con- 

 tains 20-96 per cent of 2 and 0-03 per cent of 

 C0 9 , the partial pressure of the 2 = 159-3 mm. Hg, 

 amf that of the C0 2 = 0-228 mm! Hg. To deter- 

 mine the tension of the gases of expired air, 

 whether emitted from the trachea, or at a deeper 

 level where it bifurcates with the bronchi, it is 

 sufficient to determine the percentage composition 

 of the 2 and C0 2 in the air obtained during ex- 

 piration by an air-pump attached to a simple 

 sound, the end of which can be introduced more 

 or less deeply into the respiratory passages. 



It is, on the contrary, difficult to determine 

 exactly the tension of the 2 and CO 2 of the cir- 

 culating blood, venous or arterial. Indirect methods 

 have to be employed for this purpose. 



Pfliiger and Wolffberg, to determine the tension 

 of 2 and C0 2 in venous blood circulating in the 

 pulmonary capillaries, devised the method of sound- 

 ing the lung by a very simple instrument, which 

 they called the pulmonary catheter (Fig. 170). It 

 consists of two elastic tubes, the finer of which is 

 inserted into the larger. The first has an open end, 

 intended to communicate with one of the bronchi, 

 from which air can be aspirated by means of the 

 Torricellian vacuum at the other end. The second 

 is closed, and terminates in a thin rubber balloon, 

 which can be easily inflated by a small bellows. 



Having opened the trachea of a dog, the sound 

 is introduced into the bronchus leading to the 

 inferior left lobe of the lung ; the small terminal 

 vesicle of the external tube is then inflated, so that 

 it hermetically seals the bronchus into which it is 

 introduced, and makes the corresponding lobe of 

 the lung impervious to external air, which does 

 not appreciably disturb the respiratory movements of the animal After 

 tour to five minutes the air contained within the blocked lobe of the lung 



FIG. 171. Fredericq's aero- 

 tonometer. The blood, 

 which is rendered inco- 

 agulable with peptone, 

 rises from the carotid in 

 tube a ; spreads over sur- 

 face of larger tube c, where, 

 by diffusion, it is brought 

 into equilibrium of tension 

 with the mixture of gases 

 therein contained ; and re- 

 turns by the jugular vein 

 into the animal by tube ft. 

 Tube c is covered with a 

 large tube R, within which 

 water at the temperature 

 of the animal's body is 

 kept continuously circu- 

 lating. The small lateral 

 tube t introduces the 

 artificial mixture of gases 

 into tube c at the com- 

 mencement of the experi- 

 ment. The thermometer 

 T regulates temperature 

 of water circulating in R 

 during the experiment. 



