Increased Pressure 1015 



tion, or, in other words, in the quantity of air which passes through 

 the lungs in a given time. 



The most original part of the thesis is that which relates to the 

 study of the variations in the production of urea. M. Pravaz has 

 made five experiments on this subject: 



In the first, he measures the urea voided during 24 hours first 

 at normal pressure, then under increased pressures from 10 cm. to 

 76 cm.: the urea decreased (average: from 29.6450 gm. to 28.4448 

 gm.). 



The second was performed in the same way, with the added pre- 

 caution of submitting to a fixed and regular diet: increase of urea 

 (average: from 29.1685 gm. to 31.4947 gm.). 



The third, like the second in method, gave a decrease (average: 

 from 27.2401 gm. to 26.2224 gm.) . 



In the fourth, the method was changed. The diet was the same 

 (this diet, which seems to me very low in carbon and a little ex- 

 aggerated in nitrogen, was composed of 250 gm. of bread, 200 gm. of 

 lean meat, 100 gm. of dry cheese) , but the urine was collected only 

 in the morning, fasting, for three hours, either in open air, or under 

 pressure. Here, an increase in compressed air (average: from 

 3.2019 gm. to 3.4965 gm.) . 



Finally, in the fifth, performed like the preceding one, the ex- 

 cretion of urea was studied from hour to hour during the stay in 

 compressed air; the averages are: in open air 0.9492 gm.; during 

 the first hour of compression 1.0758 gm.; during the second 1.0651 

 gm.; during the third 1.0363 gm.; in the following hour, at normal 

 pressure 0.7178 gm. ■ • 



M. Pravaz concludes from these data: 



1). That the excretion of urea increases under the influence of 

 compressed air; 



2) . That this increase is at its maximum at the beginning of the 

 compression; 



3) . That it is greater at low pressures (at about 20 cm.) than at 

 high pressures (from 30 cm. to 76 cm.). 



4) . That after the decompression there is a decrease in the pro- 

 duction of urea. 



The experiments on the exhalation of carbonic acid, relating 

 only to the percentage of this gas in the expired air, and not to the 

 quantity given off in a given time, could give no really interesting 

 result. 



Finally, M. Pravaz thinks he can conclude from his observations 

 on the temperature, that it follows exactly the same course as the 



