Theories and Experiments 459 



The increase in pressure of the ambient medium produces its 

 maximum effect upon the tissues of the periphery. These tissues be- 

 come more compact, but they resist the outer pressure to a certain 

 degree, and neutralize a fraction of it. The remaining pressure com- 

 presses the layers lying below the first ones, but it meets a new 

 resistance from them which decreases its intensity still more, and so 

 on. In proportion as one goes from the surface towards the central 

 parts, the tissues are less and less compacted, and the pressures more 

 and more weakened. But the blood contained in the superficial tissues 

 transmits the outer pressure to the whole mass of the blood, in all 

 directions, to all depths, and almost equally. Consequently, in all parts 

 of the body, the blood exerts against the walls of its vessels, from 

 within outwards, and tending to expand them, a pressure almost equal 

 to the pressure it sustains from without. 



To resist this expansion of the vessels, each tissue has its own 

 resistance and the fraction of outer pressure which has penetrated as 

 far as that through the more superficial layers. The result is that the 

 different tissues resist this expansion of the vessels very unequally, 

 and that the deeper the tissues lie the greater is the expansion, because 

 the outer pressure transmitted to the tissues by the tissues decreases 

 with the depth. Consequently: expansion of the vessels in the deep 

 tissues, where the pressure coming from the exterior is weak; decrease 

 of the diameter of the vessels in the superficial layers where the outer 

 pressure is strong; all that in a suitable measure so that equilibrium 

 may be established everywhere. At each new increase of pressure, a 

 similar effect is produced; a new distribution of blood and a new 

 equilibrium are established. The total effect is a greater mass of blood 

 in the tissues and the deep-lying organs; in a word, the visceral con- 

 gestions and the hyperemias, which all the authors mention, appear. 

 (P. 52.) 



But M. Bucquoy finds solid ground again when he speaks of 

 the painful effects of decompression. He does not have much 

 trouble in managing the theories of Pol and Watelle on the slow 

 effects of superoxygenation of the blood, and of Guerard on the 

 rheumatic nature of the pains. Considering the question as a 

 physicist, he says: 



If one enters compressed air, the oxygen, carbonic acid, and nitro- 

 gen, held in simple solution in the blood, must increase with the pres- 

 sure; and if the compression has lasted long enough, Dalton's Law 

 requires that the quantity of each of these gases absorbed by the 

 blood should be proportional to its pressure in the compressed air 

 which one is breathing. Under ordinary conditions, the carbonic acid 

 and nitrogen of the blood are not drawn in with the air inspired; they 

 are engendered by the physical phenomena of life. Because of their 

 origin, these two gases no doubt do not follow Dalton's Law strictly, 

 but their ponderable quantity in the blood necessarily varies in the 

 direction indicated by this law. 



That being granted, what must happen when one leaves the com- 

 pressed air apparatus? 



