282 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
Thus the effects of oxygen want can be completely overcome up to 
altitudes of some 8 miles by breathing pure oxygen and this is done 
in military aircraft of all nations. Above this height pressure must 
be applied in addition. In the altitude-record balloon ascents by 
Professor Piccard and by the United States Army, closed gondolas 
at raised pressure were used. 
Figure 6 illustrates the time elapsing between cutting off the oxygen 
supply to a man and his becoming unconscious at various heights. 
From this it will be realized how quickly a pilot must act should his 
oxygen supply fail at high altitudes. 
“Oot WITHOUT O2 
feed St aes, a tee eS s 
TT SE HREM GE Oe ke Dow 
FIGURE 6.—Time between changing from breathing oxygen to 
breathing air and the occurrence of unconsciousness. (After 
Ruff. ) 
The psysiological abnormalities at altitude are not entirely solved 
by breathing oxygen as there are effects on the body at low pressure 
in addition to oxygen lack. At ground level the air pressure drives 
nitrogen into the blood which dissolves in appreciable quantity. If 
now the pressure on the man is rapidly reduced before this nitrogen 
can escape,,it will form bubbles in his blood vessels and stop the 
circulation. The possibility that something of the sort might occur 
in animals at low pressures was envisaged by Robert Boyle in 1670 
who placed a viper under a bell-jar and pumped out the air; when 
the pressure was reduced he saw a bubble within the eye of the viper. 
