446 Historical 



furnished with glass plates, in which the pressure can be increased 

 or diminished: 



The animal prepared so that the capillary circulation can be seen 

 is placed in the instrument, and the apparatus itself is placed under 

 the object-glass of the microscope; then one can observe the changes 

 which a greater or less ambient pressure can cause in the capillary 

 circulation. In salamanders, frogs, their tadpoles, very young rats, 

 and young mice, the arterial, capillary, and venous circulations showed 

 no change when enduring pressure, even sudden pressure, at 2, 3, 4, 6, 

 and 8 atmospheres, and conversely. Moreover, the circulation continued 

 to go on with the same rhythm under a pressure of several centi- 

 meters of mercury in salamanders, frogs, and their tadpoles. Upon 

 placing in the apparatus very young rats and very young mice (we 

 know that mammals, during the first days of their lives, can remain 

 a few hours without breathing), we could see by the perfect sound- 

 ness of circulation in these animals then placed in a vacuum, how 

 unfounded was the opinion of the physiologists who think that with- 

 out atmospheric pressure circulation is not possible; but the atmos- 

 pheric pressure and the respiratory movements in conjunction are the 

 accessory causes of the flow of the blood, as M. Poiseuille demon- 

 strated in one of his preceding memoirs. 



Poiseuille, we see, considers at the time the effect of the increase 

 and that of the decrease of pressure upon the rapidity of the circu- 

 lation; he states that they are non-existent. 



The explanations of M. Maissiat 8 also tend to consider the two 

 questions simultaneously. We saw, in Title I (page 234), that he 

 thinks that the principal factor is the intestinal gases, the volume 

 of which must change with the pressure of the air. After consider- 

 ing their expansion as speeding up circulation and respiration, and 

 as forcing the blood to the skin, he adds: 



Opposite effects and a return of the blood towards the vessels in 

 deeper positions will be caused, if, on the contrary, the outer pressure 

 on the animal increases; the effect will be medically sedative, soothing 

 both the respiration and the circulation. (P. 254.) 



A few years later, Hervier and St.-Lager, 9 at the suggestion of 

 Pravaz, made the first experiments attempted with the purpose of 

 finding out whether the organic combustions are expedited during 

 the stay in compressed air. 



The authors reach the singular result formulated in the follow- 

 ing conclusion, a result which they do not support by any figures; 

 the method by which it is obtained and which gives not the quan- 

 tity of carbonic acid exhaled, but only its proportion in the air 

 expired, is, I must say, very faulty: 10 



The quantities of carbonic acid exhaled in compressed air rise 



