The responses to a high external temperature of two groups of normal men were studied. The first group is composed of laborers at Hoover Dam, and the second of seven laboratory workers temporarily stationed in Boulder City. These studies were made in the summer of 1932.
The history of the workmen regarding previous exposure to high temperatures before coming to Boulder City showed a satisfactory adaptation. Their adjustment to the heat at Hoover Dam was likewise satisfactory. The significant changes in the body associated with adaptation are discussed. There was a slight loss of body weight during the summer. The low nitrogen excretion in the urine, after the onset of hot weather, probably indicated a decreasing protein intake. The urinary secretion per hour was 35 per cent greater during work than during rest. The chloride excretion in the urine was above 3 grams per day. This was the amount believed to be sufficient to indicate safety from heat cramps.
Comparison of the constituents of the blood, before and after work, showed a decrease in oxygen combining capacity after work in 20 of 25 observations. No satisfactory explanation for this was offered. The serum chloride concentration increased during work in all but 3 of 25 observations. The average increase was 1.0 m.-Eq. with no observation below 102 m.-Eq. The serum protein increased in all of the subjects except two, in June, July and August.
Studies of the constituents of the blood of the laboratory workers in Boston and later in Boulder City showed an elevation of the serum protein concentration. The drop in oxygen capacity was 0.3 volume per cent. There was no appreciable effect of the changes in environment on the blood volume of the four members on whom these determinations were made. The changes in the serum electrolytes were small.