422 Historical 



night later it had risen to 21.86, while the number of inspirations un- 

 der atmospheric pressure had dropped respectively from 7.67 to 7.07, 

 6.40, 6.53, and 5.00 per minute, and the respiratory capacity on the 

 contrary had risen from 3350 cc. to 3400, 3474, 3498, and 3644. 



The experiments made on MM. de K. . . and Dr. M. . . gave the 

 same result. In the latter, the frequency of the inspirations had 

 fallen during a single experiment in compressed air from 7.6 to 6.5 

 per minute, whereas his thoracic expansion had risen from 19.28 to 

 23.02 mm., and his respiratory capacity had likewise risen from 4159 

 to 4280 cc. This result proves that under the influence of compressed 

 air the depth of the inspirations as well as the capacity of the lungs 

 increase, whereas the frequency of the inspirations diminishes in in- 

 verse proportion. 



The expansibility of the thorax, as it has been investigated up 

 to the present, is only that which corresponds to an ordinary inspira- 

 tion, not modified by the will, and as it is produced as an effect of the 

 prolonged influence of the compressed air. 



However, the modifications already noted suggest also a change 

 in the conditions of the voluntary inspirations, and this change is to 

 be verified by the increase of the total circumference and of the volun- 

 tary expansion of the thorax before and after the prolonged action of 

 the compressed air. If the capacity of the lungs had really been in- 

 creased, the last measurements should indicate an increase in the 

 circumference of the thorax, not only during the greatest expirations, 

 but also during the deepest inspirations; and if by a prolonged stay 

 in compressed air the ease of a habitually more vigorous respiration 

 had been gained, the maximum expansibility of the thorax should 

 also have increased. This result is also verified by the figures. My 

 thoracic circumference, which on April 30 after the deepest inspira- 

 tion had been 85 centimeters, was 86.5 on September 1; and after the 

 strongest expiration, it was 77 cm. on April 30, and 78 cm. on Septem- 

 ber 1; so that my pulmonary expansion was 8 centimeters on April 30, 

 and 8.5 cm. on September 1. 



The general increase of the lung capacity, as it was indicated by 

 the spirometer, and the increase of the vertical diameter of the lungs, 

 as it was determined by percussion, receive an additional demonstra- 

 tion by the increase of the thoracic circumference. 



Finally, the proportions of the respiratory periods: 



The inspiration is made more easily, being favored by the increase 

 of pressure, by the extensibility of the pulmonary tissue, and by the 

 compressibility of the intestines, whereas more force is needed for 

 the expiration so as to contract the lungs which are more distended 

 and to expel the greater quantity of air expired. That is why the 

 expiration is made with more difficulty and more slowly than in the 

 normal state. While under atmospheric pressure the duration of the 

 inspiration is to that of the expiration almost as 4:3, this ratio be- 

 comes in compressed air almost as 4:6, 4:7, and even 4:8 and 4:11. 



However the resistance to the expiration finds partial compensa- 

 tion in the more powerful contraction of the abdominal muscles 



