EVOLUTION OF HEAT. 531 



seldom very considerable. The concurrent observations of Dr. Davy, Dr. 

 W. Ogle, 1 Dr. Jiirgensen,- and Dr. Casey, 3 show that the body is wannest in 

 the morning and coldest at night. Dr. Ogle found that the temperature 

 rose from morning till late iu the afternoon, after which it fell till bedtime. 

 The lowest temperature occurred about daybreak. The average diurnal 

 variation was about 1.5 Fahr. The minimum temperature noticed was 97 

 at 5.30 A.M., in winter. The maximum was 100.6, whilst in a Turkish bath 

 of 120. The extreme oscillation of temperature, therefore, was not more 

 than 3.5 F. in health. Dr. Jiirgenseu found the diurnal variation to amount 

 to from 1.8 to 3.6 F. ; the minimum occurred from 1.30 A.M. to 7.30. The 

 temperature then, with some fluctuation, rose till 4 P.M., when it attained its 

 maximum, which lasted till 9 P.M.; and after this it again fell. Dr. Casey 

 found his mean temperature during the day to be 98.07 F., the mean range 

 of temperature 1.61 F. The maximum range 2.5. The maximum tem- 

 perature was at 7.30 P.M. Sydney Ringer and P. Stewart 4 give the average 

 maximum temperature for persons under twenty-five years of age at 99.1 

 Fahr., of those over forty 98.8 F. They find the period of highest tem- 

 perature extends from 9 A.M. till 6 P.M., the lowest is about midnight. These 

 observations correspond well with what has already been pointed out with 

 regard to the relative activity of the respiration ( 311, viii and ix) and 

 circulation at different periods of the twenty-four hours. As a rule the 

 temperature of the two sides of the body is alike, but Blake 5 has observed 

 that the right side is sometimes as much as 1 F. higher than the left during 

 exertion, especially in the sun. 



in. That an increase in the heat of the body is produced by exercise, and 

 that repose tends to its reduction, is a matter of familiar experience ; but 

 the observations of Dr. Davy show that there is scarcely any perceptible dif- 

 ference iu the heat of the deepseated parts, the augmentation and depres- 

 sion being confined to the extremities. Thus, on one occasion recorded by 

 him, the temperature of the air of the room before walking being 60, that 

 of the feet (shown by a thermometer placed between the toes) being only 

 66, that of the thermometer under the tongue being 98, and that of the 

 urine being 100, the temperature after a walk iu the open air at 40, the 

 exercise having diffused a feeling of gentle warmth through the body, was 

 96.5 in the feet, 97 in the hands, 98 under the tongue, and 101 m the 

 urine. So, on another occasion, the temperature having been 66 in the 

 room, 75 in the feet, 81 in the hands, 98 under the tongue, and 100 in 

 the urine, after a walk in air at 50 the temperature was 99 in the feet, 

 98 in the hands, 98 under the tongue, and 101.5 in the urine. These 

 effects are, therefore, in all probability, chiefly due to an increase in the 

 energy and frequency of the heart's contractions, by which means the warm 

 blood is driven with greater velocity through the extreme capillaries, im- 

 parting its heat to the surrounding parts. Marcet 6 found in the ascent of 

 Mont Blanc that when at rest the temperature of the body did not vary 



: St. George's Hospital Reports, vol. i, p. 221. Dr. Ogle's experiments were made 

 on two healthy adults ; the temperature being taken by introducing a warmed self- 

 registering thermometer three or four times a day under the tongue, and retaining it 

 in that position for several minutes. They extended over a year. 



2 Deutsches Archiv f. Klin. Med., Bd. iii, p. 166. Dr. Jiirgensen's experiments 

 extended over three days, and consisted in reading off at intervals of five minutes the 

 indications of a thermometer permanently retained in the rectum at a depth of about 

 two inches. 



3 Lancet, vol. i, 1873, p. 200. 4 Proceed, of the Roy. Soc., vol. xvii, p. 287. 



5 E. Blake, Med. Times and Gazette, Oct. 1871. 



6 Archiv. des Sci. Physiques, t. xxxvi, p. 247. 



