Compressed Air; Low Pressures 



773 



be taken are to ventilate the bell properly before inserting the 

 stopper, to make a record only when the animal is very calm, and 

 for compressed air, to avoid variations of pressure during the 

 recording. 



Experiment CCCXXXIV. February 12. A cat is placed under the 

 bell. 



At normal pressure it gives the tracing in Figure 67. 



We take it into the compression cylinder and in about an hour, 

 reach a compression of +53 cm. (total pressure 128 cm.) We then 

 obtain the tracing in Figure 68. 



Examination of these two tracings shows: 1) that the number 

 of respirations has diminished (in the proportion of 10 to 7) ; 2) that 

 the amplitude of the oscillations has likewise diminished, that is, 

 that the variations of the intra-thoracic air pressure were less in 

 compressed air than at normal pressure. 



F. Arterial Pressure. 



The increase of the arterial pressure under the influence of com- 

 pressed air has been admitted on the strength of the sphymographic 

 tracings of Vivenot; but no direct experiment had been made, or 

 rather had succeeded, in the aim of ascertaining by the manometer 

 the direction and the amount of the modification. 



I have tried to fill this gap by the following experiments. 



Experiment CCCXXXV. February 17. Dog of average size, new 

 subject, fastened upon the dog board. 



Ludwig's recording manometer, attached to a cannulated femoral 

 artery, gives the tracing of Figure 69, in which the low points are 

 5.5 cm. above the zero line, which indicates a pressure of 11 cm., and 



Fig. 69 — Tension of the blood in the femoral artery. Normal pressure. 



Fig. 70 — Tension of the blood in the femoral artery. Compressed air. 



