HUMAN LIMITS IN FLIGHT—MATTHEWS 281 
gator, ‘realizing what had happened, was in time to stop him from 
climbing out of the machine, take over the controls and reconnect the 
pilot’s breathing apparatus. It is easy to see that such an incident 
might not always have a happy ending. The effects of oxygen want 
may often be extremely amusing but clearly there is no place for such 
events in the dangerous and difficult work of high-altitude flying. 
There are two ways in which altitude effects can be overcome. The 
first is to increase the amount of oxygen in the air which the pilot 
breathes by mixing oxygen from gas cylinders with it, thus giving the 
pilot a mixture rich in oxygen or even pure oxygen to breathe. In this 
way when the pressure is one-quarter of an atmosphere at 33,000 feet 
if his lungs are filled with pure oxygen he will not suffer from any 
symptoms of oxygen lack. To this end the pilot always wears an 
oxygen mask, which also carries a microphone for his communication 
with the crew or ground. 
The second alternative is to increase the amount of oxygen in the 
pilot’s lungs by compressing the air in them. Im an engine the loss 
of power from oxygen lack is overcome by compressing the thin 
air with a supercharger, but it is not possible to supercharge the lungs 
so easily as the pressures required would burst them. The pilot must 
therefore be completely surrounded by air at increased pressure, 
This can be done either with a pressure suit something like a diving 
dress or, if the cabin is sealed and made strong enough for it to 
withstand a raised air pressure, produced by a pump attached to the 
engine. The air around the pilot can then be kept at 14 lb./sq. in. 
and the atmosphere he breathes can be exactly like that at ground 
level. However, it is clear that for military use such a pressure 
cabin is very vulnerable, though for civil use it is the ideal method 
in high flying because the passenger is not inconvenienced by a mask 
on his face and need not be aware, by any change in the air pressure, 
that he has left the ground. Some pressure cabins are in use in civil 
airlines in America. The pressure cabin has other advantages over 
the oxygen mask besides preventing lack of oxygen. At heights up 
to 36,000 feet a man can avoid oxygen lack by breathing pure oxygen, 
but above 44,000 feet even breathing pure oxygen he would become 
unconscious. Moreover the vapor pressure of blood equals the at- 
mospheric pressure at 63,000 feet so if a man could reach this pressure 
his blood would boil and his lungs be filled with steam. At heights 
above 40,000 feet it becomes necessary not only to breathe pure oxygen 
but also to increase the pressure acting on man. Plate 2, figure 1 
shows the machine and pressure suit in which Flight Lieutenant 
Adam broke the world’s altitude record by reaching 54,000 feet in 
1937. The suit. was blown up to some 214 lb./sq. in. pressure and 
filled with pure oxygen. In it man could survive even in a vacuum. 
