394 OF RESPIRATION. 



corresponded in its variations to that of the Carbonic acid, being 21.7 

 grammes by day and 15.5 grammes by night. 



312. The effects of exposure to increased atmospheric pressure have been 

 made the subject of experiment by Vivenot, 1 C. W. Miiller, 2 Paul Bert, 3 and 

 Pan urn, 4 but have best been illustrated by the observations made by Dr. 

 Jaminet 5 on himself and on the workmen engaged in the construction of the 

 Illinois and St. Louis Bridge over the Mississippi River. In the course of 

 this work the men were engaged in excavations conducted at a depth of 115 

 feet below the level of the surface of the river, the pressure of the air then 

 amounting to upwards of fifty pounds on the square inch of their bodies, ex- 

 clusive of the ordinary atmospheric pressure of fifteen pounds on the square 

 inch. No ill effects were observed, even when the pressure was greatest, 

 whilst the men were working in the air-chambers; it w-as only on suddenly 

 emerging that great exhaustion, pain in the epigastrium and spine, sickness, 

 paraplegia, involving the bladder and rectum, and even death occurred. 

 Great care was taken that on entering and leaving the air-chambers the 

 workmen should remain for ten minutes or more in lock chambers, in which 

 the pressure was gradually increased or diminished. The pulse and respira- 

 tion usually rose in frequency on exposure to the augmented pressure, and 

 free perspiration occurred ; but it must be remembered that the air-chambers 

 were small, and the temperature in them was many degrees above that of the 

 open air. The Urine and Urea were at the same time increased. Speaking 

 generally, there seems to be reason for believing that under the conditions 

 to which the men were here subject, with moderate pressure (20 Ibs. to the 

 square inch), the activity of the physiological functions was augmented, 

 though there seemed to be a reaction on return to ordinary pressure. 

 In the cases in which death occurred, the Brain and Spinal Cord were found 

 to be highly congested, and their cavities filled with serum. M. Vivenot's 

 experiments found that an increase of pressure amounting to one-fifth of the 

 normal decreased the respiration two, and the pulsations ten per minute. 

 The proportion of gases contained in the blood is only to a slight extent de- 

 pendent on the pressure. 6 The recent experiments of M. P. Bert 7 have, how- 

 ever, shown that when animals are made to respire pure oxygen gas under 

 a pressure of five or six atmospheres (or, which is the same thing, when the 

 pressure of the ordinary air is raised to 20 atmospheres) it acts like a poison 

 convulsions resembling those produced by strychnia occurring. These set 

 in, in dogs, when the blood contains about 10 per cent, more oxygen than 

 normal, and it is remarkable that the convulsions continue after the animal 

 has been withdrawn from the pressure and its blood only contains the usual 

 proportion of oxygen. The effects of diminution of pressure in some respects 

 resemble those of exalted pressure. Thus Hoppe 8 observed that when rats were 

 placed under the receiver of an air-pump and exhaustion made till the pressure 

 was reduced to 2 inches of mercury, fainting and convulsion were induced, 

 and when it was reduced to 1:] in. (40 mm.), death occurred, apparently 

 from the evolution of gas in the capillaries of the lungs, which impeded the 

 passage of the blood. The singular effects observed by Glaisher' in his lofty 



1 Virchow's Arcliiv, Bd. xxxiii. 2 Zeitschrift fur rat. Mcd., Bd. xxxiii. 



3 Complcs Rendus, t. Ixxiii, pp. 213, 503, and Li^ons sur In Respiration. 



4 Piliur.-r's Archiv, Bd i. 



6 Physical Ktleets of Compressed Air observed in the Construction of the Illinois 

 and St. Louis Mrid^o, 1871. 



6 Matliiru and Urbain, Comptes Rendus, 1871, p. 210. 



7 Ct'inptcs Udidiis do 1'Acad dcs Sciences, 1872-73. 

 1 Miill.-r's Archiv, 1857, p. 63. 



9 Glaisher, Art. Aeronautics, Encyclop. Britannica, 1875, p. 167. 



