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Show 328 APPENDIX H 15. ON THE PHYSIOLOGICAL EFFECTS OF A VERT HOT CLIIMATE, BY DR. O. LOKW. UNITED STATES ENGINEER OFFICE, GEOGRAPHICAL SURVEYS WEST OF ONE HUNDREDTH MERIDIAN, Washington, D. C, February 9,1876. DEAR SIR : I have the honor to submit herewith a report upon the physiological effects of a hot and dry climate, a subject deserving attention in connection with the exploration or occupation of the Colorado Valley, and one not heretofore treated upon to any great extent. Very respectfully, your obedient servant, OSCAR LOEW. Lieut. GEO. M. WHEELER, Corps of Engineers, in Charge, It is in but comparatively few regions of the earth that the temperature of the air rises above blood- neat for weeks and months in succession ; hence, our knowledge of the physiological changes produced by it are quite meager. When it is considered that under ordinary circumstances the whole tendency of the human system is directed toward keeping its temperature above that of the surrounding air, the task is suddenly reversed in the hot deserts, where the thermometer rises for considerable periods daily up to 110° to 116° F., in some cases up to 120°, while the normal temperature of the blood is 98°. 5 P. That this task is at first not solved with precision is because the system only gradually accommodates itself entirely to the new • conditions, and apparently after losing twelve to fifteen per cent, of its bodily weight. What a change in the conception of hot and cool is undergone in such a climate, when it is found agreeably oool in the evening, when the thermometer has descended from J10° to 94° F. 1 Observations on pulsation and respiration were frequently made, and it was found that the former' was generally much increased, while the latter showed but a slight, sometimes no increase. The following table shows some of these observations: _ A B c D E F G H July 30. Pulsation. 75 78 73 80 76 56 79 96 Respiration. S3 16 19 14 18 19 18 18 July 31. Pulsation. 60 89 80 65 79 60 Respiration. 18 SS SI 93 28 17 The temperature of the air was 108° F. in the afternoon when the observations were made. G and H were two Payute Indians, who came into camp, one of about twenty-five, the other about sixty years of age. On July 31, a hot wind was blowing all the afternoon, and the observations were made after a march of 15 miles to El Dorado Cafion, on the Colorado River. A, B, and C, were at work upon the mesa and exposed to the hot sun and . wind, while D, £ , and F had taken a bath iu the river and remained in the cool shade on the shore. F was a very phlegmatic person, and his pulsation and respiration were always lower than the others. The normal number of respirations during the day is considered to be 18 per minute; that of pulsation 60 per minute. The temperature of the body was taken on various occasions and found, to be increased in very hot afternoons about 1° F., but at one time, after a march of 20 miles in a scorching heat, it was found with B increased fully 2°, ( taken under the tongue.) If it is considered that the temperature of the body is but 98.° 5 F., it must be a matter of surprise that in a heat of 110° to 116° F. it is not increased more than one or two degrees above the normal temperature, although inner heat is being produced by breathing and oxidation that is continually going on in the blood. The system has, therefore, to contest against two sources of heat, the interior and the exterior. That a decrease in the assimilation of food forms one condition is doubtless true; but he principal factor is an enormous evaporation from the body, which to determine |