182 AIR AND LIFE. 



Another cause also operates, in the case of fishes or other aquatic 

 animals that live at great depths, when they happen to rise too near 

 the surface, thus coming from high to low pressure. The gases of the 

 body, dissolved in the liquids (blood, etc.), have a higher tension than 

 the outside pressure, and the result is that these gases expand and 

 burst the tissues within which they are contained when the exterior 

 pressure becomes less than that which reigns in the interior. The case 

 is exactly that of a bladder inflated with air placed in the receiver of 

 an air pump; if the air of the cylinder is gradually exhausted, the blad- 

 der swells until it explodes. This is an extreme case, which hardly 

 occurs under natural conditions, but other accidents of a similar 

 nature, which are explained by the same mechanism, often do occur 

 in man or animals, as we shall show further on. 



We can not leave this subject without adding a few words concern- 

 ing mountain sickness. It is a well known fact that at the same alti- 

 tude different aeronauts or tourists are not equally affected. Of course 

 this statement refers only to moderate altitudes, between 3,000 and 

 4,000 meters. At the very same place, on the same day, one person is 

 a victim to mountain sickness and another is not. As only individuals 

 of the same species are compared, the reason of the difference can only 

 lie in personal or individual peculiarities; no specific physiological 

 differences can exist such as those met with when one compares the 

 influence of one and the same agency or poison, etc., upon individuals 

 of different species; there is no evident and tangible cause such as 

 that which one detects when comparing the resistance of the duck and 

 of the common fowl to submersion, when the greater resistance of the 

 former is due to its greater amount of blood, and consequently more 

 considerable provision of oxygen. There are doubtless physiological 

 differences of real importance between different individuals belonging 

 to the same species, and between different varieties of the same spe- 

 cies; considered in toto those differences are more important and more 

 frequent than commonly supposed, and probably more important than 

 those external morphological characters which are the bases of classi- 

 fication at present. But such important differences can not obtain 

 between two individuals belonging to the same species, and the fact 

 that they may occur one day and be wanting a week later, shows that 

 they are merely accidental and temporary. 



Mountain sickness is due to a condition of asphyxia, as already 

 noticed, and this fact explains the differences referred to, as an ingen- 

 ious experiment performed by M. Paul Eegnard amply shows. This 

 experiment was suggested by the proposal, made by a company, to 

 build a lift by which to reach the top of the Jungfrau, the well-known 

 Alpine peak. Before setting to work,, it was desirable to ascertain 

 whether the passage from low to high altitude would not produce 

 unpleasant symptoms in the tourists using the lift, 1 and to show that 



'The lift -was to bo established in vertical shafts from a horizontal tunnel at the 

 base of the mountain to the top. 



