Medical Apparatuses 421 



tional to their amplitude, so that while this amplitude increases, the 

 frequency of the respiration diminishes. The increases of the capacity 

 of the lungs, under the effect of compressed air, is the cause of the 

 slackening of the -respiration; or, in other words, the slackening of the 

 respiration is an inevitable consequence of the increase of the pul- 

 monary capacity, because the inspiration and expiration of a greater 

 volume of air necessarily require more time. 

 Then the depth: 



We could imagine three different methods as possible. A com- 

 pensation might be established between the frequency and the depth 

 of the inspirations by the fact that the amplitude of the respiration 

 could be less than under normal pressure, since a greater quantity of 

 air enters in the same volume, and the frequency of the respiration 

 could nevertheless be reduced also; or, in the second place, the com- 

 pensation could be established, for the same reasons, by less numerous 

 inspirations, keeping the same amplitude. Finally, in the third place, 

 there might be, in spite of the supplying of a greater quantity of air, 

 as a consequence of the compression, a slowing down and an increase 

 in depth of the inspirations. This last condition appeared a priori 

 most probable if we took into account the increase in amplitude of 

 the respiration, as we had observed it, and it should occur particularly 

 in persons whose pulmonary capacity had been pathologically reduced. 



To settle these questions, I used an apparatus constructed for the 

 purpose, which could be attached around the thorax, and followed 

 its movements of inspiration and expiration, the increase of the cir- 

 cumference of the thorax being indicated in millimeters by the sep- 

 aration of two movable needles. This greater or smaller increase in 

 the thoracic circumference served to measure the greater or smaller 

 depth of the inspirations. In each of the thirty-nine experiments 

 made with this thoracometer, the depth and the number of the in- 

 spirations were noted for fifteen consecutive minutes, long enough 

 for the effect of the will or a slight error of observation to be negli- 

 gible. The experiments were always made comparatively in atmos- 

 pheric air and in compressed air; and as the frequency of my inspira- 

 tions was then from 7.67 to 4.40 per minute, from 115 to 66 observa- 

 tions were needed in each experiment, making a total of about 3000 

 numbers concerning the mobility of the thorax. 



The measurement made as explained above justifies the state- 

 ment that in me, on the first day of the experiment, the thoracic 

 expansion, that is, the increase of the thoracic circumference produced 

 by an ordinary inspiration was 12.39 mm. at normal pressure, and 

 at the beginning of the maximum pressure 15.68; after an hour of 

 this same pressure 17.22; and at the end, under normal pressure 

 18.14, whereas the frequency of the inspirations had dropped from 

 7.67 to 6.07, 5.80, and even 5.60; there had been produced therefore 

 under the influence of the compressed air a progressive decrease of 

 frequency at the same time as a progressive increase in the depth of 

 the inspirations, which continued even after ordinary pressure had 

 been restored. The next day, the thoracic expansion under normal 

 pressure was 14.92; the third day, 17.84; the fifth day, 18.98; a fort- 



