THE MARCH OF MEDICINE—WINTROBE 391 
flies, and 10 species known to be vectors of 6 different animal diseases. 
Rats have also been found in aircraft. It has been shown that mos- 
quitoes may survive journeys of over 9,500 miles lasting for 614 days 
and that some of them though frozen on arrival have revived when 
they became warm again. 
The danger lies not so much in infected insects biting several indi- 
viduals and causing illness thereby, but in the possibility of their 
becoming established in the new region to which they have been trans- 
ported. This occurred in Brazil and required much effort and expense 
to eradicate. The transportation of freight by aircraft will probably 
greatly facilitate the transfer of infected small animals, like rats. 
Our own Public Health Service has been fully conscious of the 
possibilities of this mode of transmission of disease and measures had 
already been taken before the war to meet some of the problems which 
had been raised. Undoubtedly, however, with the rapid expansion 
of air transportation, vigilance will have to be keen if serious trouble 
is to be prevented. 
Necessity has caused a new branch of medicine to develop to an 
unprecedented degree. The airplane of today functions better in the 
air than the man who flies it. The exploitation of all the possibilities 
of these extraordinary machines has been quite definitely hampered 
by the limitations of man’s capacity for adjustment to unusual condi- 
tions. It has been the task of aviation medicine to find ways of 
adjustment to changes of barometric pressure, to reduction of air 
pressure, and to extraordinarily rapid changes in direction and accel- 
eration. This has required an expansion of the study of physiology 
which will be valuable in many ways besides those related to flying. 
It was learned in World War I that 90 percent of the accidents in 
the air were due to errors of the pilot and that in some squadrons 50 
percent of the pilots were suffering from a neurosis which made them 
actually unfit for duty, though they continued to fly anyway. The 
problem has been enormously magnified in the present war. 
Decreases in atmospheric pressure with increasing altitude are re- 
sponsible for two of the major difficulties of the flier, namely the 
expansion of gases contained in the cavities, tissues, and fluids of his 
body and the effects of lack of oxygen or anoxia. Although the body 
is capable of making some adjustments to the effects of changes in 
barometric pressure, these cannot be made as quickly as our present 
machines are capable of rising. 
One source of trouble is the expansion of intestinal gases. At 18,000 
feet their volume is doubled as compared with that at sea level and at 
33,/00 feet it is quadrupled. With rapid rates of ascent these gases, 
instead of being eliminated, get caught in the intestinal loops and 
produce severe abdominal cramps. There is also the problem of the 
