ALTHOUGH the effects of decompression sickness as observed in caisson disease have been well known for many years, interest in this problem has recently been revived in connection with development of the same illness in aviators on ascent to high altitudes. Opportunity for studying this condition was provided during the training of approximately 470,000 airmen for flight to high altitude. In only 6 of this very large number of men did reactions or conditions develop directly or incidentally related to this training which resulted in fatalities. In the course of this training, trainees undergo a simulated "flight" in a decompression chamber. The pressure in this chamber is reduced in order to simulate high altitude, and the subject is instructed in the use of his equipment under these conditions.1 If severe symptoms of decompression sickness develop, the subject is immediately returned to ground level for treatment and observation. In this