392 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
expansion of nitrogen, which constitutes 78 percent of the air. This 
gas is dissolved in the body fluids in proportion to its partial pressure. 
When this pressure is reduced on ascending to a high altitude, if suffi- 
cient time is allowed the excess of dissolved nitrogen is brought by the 
blood to the lungs and is blown off. If ascent is very rapid, however, 
the gas is liberated before it reaches the lungs. Bubbles form in all 
the tissues with the result that the joints become stiff and sore, motion 
becomes impaired or is even totally inhibited (the “bends”), the skin 
itches and burns and giant hives may appear, and severe neuritic pain 
may develop owing to the large proportion of nitrogen which tends 
to accumulate in the fatty tissues of the nervous system. Bubbles form- 
ing in the brain may produce convulsions, paralysis, and even death. 
One of the most distressing and dangerous complications is “the 
chokes,” in which a burning sensation develops under the breast bone, 
followed by stabbing pain and progressive inability to breathe nor- 
mally without coughing. Under combat conditions, as for example in 
interceptor planes which must take off at a moment’s notice, there is 
often insufficient time for adequate desaturation. 
The effects of lack of oxygen are insidious and not easily detected. 
Up to 10,000 feet the flier notices nothing except perhaps some in- 
crease in the rate and depth of respiration. A vague feeling of un- 
easiness may appear, the breathing becomes deeper and the pulse 
more rapid. Between 15,000 and 18,000 feet if he stays there for more 
than a couple of hours the flier is likely to experience severe headache, 
nausea and vomiting. Even with shorter exposures at this altitude, 
certain important mental changes occur. He may become rather de- 
pressed, sleepy and tired or elated, hilarious and aggressive, even pug- 
nacious. He may not remember what his course is supposed to be but 
he does not care. There is a marked resemblance to alcoholic intoxica- 
tion. “Time sense is impaired and hours seem like minutes or vice 
versa. If he must perform any calculations, he finds that simple arith- 
metic is too much for him and his trembling pencil makes distorted 
figures on the paper. As he climbs above 20,000 feet his handwriting 
becomes a meaningless scrawl. His field of vision is constricted, the 
sky looks dark and the noise of the engine may be nearly inaudible. 
He is eventually unable to move a muscle and, at about 25,000 feet he 
passes into coma.” (6) These ill effects can be met in large measure by 
the inhalation of oxygen. Regulations make its use compulsory above 
10,000 feet. Unfortunately, however, some pilots in spite of rules see 
no reason for taking oxygen as long as they feel all right. Too many 
fail to realize that probably the most dangerous feature of oxygen want 
is the insidiousness of its approach. 
The availability of oxygen through tanks is only one factor. At 
40.000 feet, where planes are now flying, adequate oxygenation of the 
