616 



EVOLUTION OF HEAT, LIGHT, AND ELECTRICITY. 



being entirely dependent (as in Plants) upon the degree of external warmth to 

 which their bodies are subjected. We shall now inquire, in the first place, into 

 the amount of Heat thus generated by Man ; and then into the sources of its 

 production. 



651. Our present knowledge of the ordinary Temperature of the Human 

 body under different circumstances is chiefly due to the investigations of Dr. 

 J. Davy. 1 The first series of his observations included 114 individuals of both 

 sexes, of different ages, and among various races, in different latitudes, and under 

 various temperatures; the external temperature, however, was in no instance 

 very low, and the variations were by no means extreme. The mean of the ages 

 of all the individuals was 27 years. The following is a general statement of 

 the results, the temperature of the body having been ascertained- by a thermo- 

 meter placed under the tongue : 



Temperature of the air 60 

 69 

 78 

 79.5 

 80 

 82 



Mean of all the experiments 74 

 Highest temperature of air 82 

 Lowest temperature of air 60 



Average temperature of the body 



Mean of all the experiments 

 Highest temperature of body 

 Lowest temperature of body 



98.28 



98.15 



98.85 



99.21 



99.67 



99.9 



100 



102 



96.5 



From this we see that the variations noted by Dr. Davy, which were evidently 

 in part the consequence of variations in external temperature, but which were 

 also partly attributable to individual peculiarities, amounted to 5 degrees; the 

 lower extreme might be found to undergo still further depression, if the inquiries 

 were carried on in very cold climates. Dr. Davy's subsequent inquiries have 

 been directed to the determination of the various influences which tend to pro- 

 duce a departure from the average; and it will be advantageous to present his 

 results in a systematized form, in combination with those of other observers. 

 The most important of these variations seem to be those dependent upon Age, 

 Period of the Day, Exercise or Repose, Ingestion of Food or Drink, and Ex- 

 ternal Temperature. 



a. The temperature of Infants, according to the observations of Dr. Davy, 

 M. Roger, 3 and of Dr. Gr. C. Holland, 3 is somewhat higher than that of adults, 4 

 provided that they are placed in conditions favorable to its sustenance ; but, as 

 will be shown hereafter, infants and young children are very inferior to adults 

 in their power of resisting the depressing influenced external cold ( 664). 

 Their temperature, when examined immediately after birth by a thermometer 

 in the axilla, is nearly 100; but it quickly falls to about 95.5, and gradually 

 rises in the course of the next twenty-four hours to about 97.7 in weakly sub- 

 jects, and to 99.5 in strong infants. Between four months and six years of 

 age, M. Roger found the average temperature to be 98.9 ; and between six and 

 fourteen years of age, 99.16. The temperature of aged persons, from the ob- 

 servations of Dr. J. Davy, does not seem to be below that of persons in the 

 vigor of life, provided that there be no external depressing influences : but they 



1 See his successive Memoirs in the "Philosophical Transactions" for 1814 (republished 

 in Dr. D.'s "Anatomical and Physiological Researches"), 1844, 1845, and 1850. 



2 " Archiv. G6n. de Me"d.," 1844. 



8 "Inquiry into the Laws of Life," 1829. 



4 Dr. W. F. Edwards ("On the Influence of Physical Agents on Life," p. 115) gives as 

 the result of his observations, which were only ten in number, that the temperature of 

 infants is lower than that stated above ; but it is obvious that these observations were 

 made during the period of depression which occurs in the first days, whilst the respiratory 

 function is becoming established. 



