536 Experiments 



the animal's breathing; but the chemical alteration of the air 

 which is the consequence becomes less and less important, as we 

 have seen, in proportion as the pressure diminishes; and so, at 

 about 15 centimeters of pressure, death occurs in pure air: it even 

 occurs as I have often observed, in an air current, and the con- 

 finement, the chemical change, are evidently not factors. 



If the various disturbances, whose details will be given later, 

 which begin to appear when the pressure is lowered to 30 centi- 

 meters; if the serious symptoms, which occur at about 25 centi- 

 meters; if death, which ensues at about 18 centimeters, are all really 

 due to the weak oxygen tension at these various periods, we should 

 be able to avert them by increasing this tension suitably, without, 

 however, changing the barometric pressure. 



Super-oxygenated air: very low pressures. This is easily se- 

 cured by using artificial air sufficiently rich in oxygen. If, in the 



2 x P 



expression which represents the oxygen tension, the per- 



76 



centage of O, increases in the same proportion as pressure P de- 

 creases, the amount of the tension will remain constant; if this 

 amount is sufficient, it should produce no disturbance in the ex- 

 perimental animal. For example, if we pass to a half-atmosphere, 

 to keep the oxygen tension in ordinary air at normal pressure, we 

 must double the amount 20.9 and use an artificial air containing 

 41.8 per cent oxygen. 



I shall give details of this important point in another part of 

 this work. But here, where we are considering nothing but death 

 in closed vessels, under different low pressures, the result should 

 be expressed in another way. If our hypothesis is true, we shall 

 arrive at the following formula: Whatever the pressure employed, 

 whatever the composition of the artificial air, the death of the 

 sparrows will always occur when the final tension of the oxygen 

 falls to about the average amount previously established, that is, 

 3.6. 



The experimental procedure was as follows: After the bird 

 had been placed under one of the bell- jars of the apparatus repre- 

 sented in Figure 15, I lowered the pressure in the bell-jar 30 to 40 

 cm., which seems to have no immediate harmful effect on the birds, 

 as we saw above. Moreover, I immediately connected cock M with 

 a gasometer filled with oxygen, and allowed this gas to enter so as 

 to restore normal pressure. Then I began again to lower the 

 pressure of this mixture already more oxygenated than ordinary 



