468 Historical 



pact tissues. That explains the increase in the vertical diameter of 

 the lungs and their displacement downward. 



The modifications which the action of compressed air can cause 

 in the gaseous exchanges of respiration were studied by Vivenot 

 with a profusion of detail; the paramount importance of this phase 

 of the question compels us to quote here a great part of his memoir 

 of 1865: 



As a basis of observations, it was necessary to determine the 

 quantity of carbonic acid exhaled in respiration, in order to see 

 whether the quantity of oxygen absorbed and the quantity of oxygen 

 consumed differ as a result of the compressed air. 



A priori, one might expect an increase in the absolute and relative 

 quantities of oxygen absorbed; in the absolute quantity, because of 

 the increase of the pressure exerted upon the lungs, and also because 

 of the previously mentioned increase of the pulmonary capacity; in 

 the relative quantity, because the number of respirations is decreased, 

 and because it has been proved that the carbonic acid exhaled, and 

 sometimes also the oxygen absorbed, are in inverse proportion to the 

 frequency of the respiration. (Vierordt) 



Vivenot then describes the spirometer which he used, and into 

 which "was exhaled the air coming from an expiration as strong as 

 possible, but made without great effort": 



If we are to have any confidence in the result, the expiration, as 

 previous attempts have proved to us, must always be made in almost 

 identical circumstances. That is why the greatest precautions have 

 been taken, and experiments were made on inspirations as deep as 

 possible, made at intervals of one hour and under absolutely similar 

 conditions. 



In my case, the volume of air was on the average 3,700 cc. The 

 duration of the respiration was from 15 to 18 seconds. The first test 

 was made one hour before entering the compressed air, that is, at 

 eight o'clock in the morning; the figures obtained at that time are not 

 important, since they were to serve only as a point of departure for 

 the experiment. The second test was made at nine o'clock, imme- 

 diately before entering the pneumatic apparatus; the third at ten 

 o'clock, under the influence of compressed air, after one hour of 

 compression; the fourth at eleven o'clock, at normal pressure, imme- 

 diately after leaving the apparatus; the fifth and the sixth at noon 

 and one o'clock, also at ordinary pressure. 



Observations made in this way, daily, from August 26 to Septem- 

 ber 13 inclusive, gave the following figures, as quantities of carbonic 

 acid expressed in grams, contained in each expiration, and correspond- 

 ing quantities of carbon exhaled. 



