528 Experiments 



rows occurs when the tension of the oxygen, measured by the 

 method that has just been specified, is represented by a number 

 varying between 3 and 4, which we can call k. 



If we refer now to line O of Figure 17, we see that each of its 



points corresponds to the equation — = k, therefore xy = 76k. 



76 



Now k having a value which varies from 3 to 4.3, taking 3.6 as an 

 average, for the point which corresponds to 41 cm. of pressure, for 



41 x 6.5 



example, the equation will be = 3.6. In other words, it is 



76 



the equation of a hyperbola having for asymptotes the axis of the 

 x's and a parallel to the axis of the y's at the zero of pressures, or, 

 to use an exact expression, of an equilateral hyperbola. 



These facts show us under a new aspect the action of the diminu- 

 tion of pressure upon the organism. They tend to show that it 

 consists principally of diminishing the exterior tension of the 

 oxygen, and, consequently, of placing the animal in conditions 

 similar to those which would be given it by respiration at normal 

 pressure in a medium containing less oxygen than the air. We 

 could even state already that no other important element is in- 

 volved, since at pressures from 20 cm. to 25 cm. we find again in 

 the table the figures 3.1 or 3.3, which indicate an exhaustion as 

 great as at normal pressure. 



Continuing this reasoning, we can determine the lower limit of 

 pressure which it will not be possible to pass without killing the 

 animals (we are still speaking of sparrows) . It will be given by 



x x 



the formula 20.9 x — = 3 and 20.9 x — = 4.3, since 3 and 4.3 are 

 76 76 



the extreme numbers given us by the experiments reported above. 



4.3 cm. x 76 



We reach thus the equation x = = 15.6 cm. for the 



20.9 



highest figure, and for the lowest, x = 10.9 cm. 



But it is clear that, to reach such low pressures, we must take 

 the greatest precautions, and slowly accustom the animal to this 

 asphyxia of a new kind. A sudden change surprising it with too 

 great an oxygen consumption would kill it, and that very thing 



