178 DIUENAL VAEIATIONS OF HEAT. 



on the respiration. In fevers it will rise to 105 ; in tetanus it may reach 

 110; the contrary in asthma, when it may sink to 82, owing to imper- 

 fect access of air ; in cyanosis to 77, owing to imperfect aeration of the 

 blood ; in Asiatic cholera to 75, owing to the non-reception of oxygen by 

 the cells in their diseased state. It also varies with the period of life : 

 in the new-born infant it is 100 ; it presently sinks to 99, and rises 

 during childhood to 102. Mental exercise in the adult increases it, 

 bodily exertion still more. The special degree varies with the point on 

 which the observation is made : the limbs are colder than the trunk, and 

 this is the more marked as the point is more remote. On the leg the 

 temperature may be 93 ; on the sole of the foot, 90 ; while that of the 

 viscera is 101. 



In his residence in different climates, man is exposed to variations of 

 Resistance of temperature which extend over a scale of 200. Toward 



1 anHrTtT ex" ^ P* GS ^ co ^ ^ winter ^ s ^ ten 60 ; in the tropics 

 tremes of tem- the heat of summer +130. For a short period his power of 

 perature. resistance is greatly beyond what these numbers would in- 

 dicate; he can enter with impunity an oven heated to 600, provided the 

 air is dry. In these cases, though excessive evaporation from the skin 

 moderates the effect and keeps it within bounds, there is always a mark- 

 ed rise of temperature of the whole body. In a corresponding manner, 

 exposure to cold produces depression, as shown in Dr. Davy's observa- 

 tions. At 92 of the air, a thermometer under the tongue stood at 100 J ; 

 at 73 it stood at 99 ; at. 60 it stood at 97J . 



Among these variations there is one class which calls for critical at- 

 Diurnal varia- t ent i n - I* ^ the diurnal variation ; less marked in man, 

 tion in the heat who instinctively makes provision against it, but well shown 

 in the case of fasting animals. This illustrates, in an inter- 

 esting manner, the controlling influence of external conditions ; for if ex- 

 posure to a high temperature, as that of an oven, compels a ^rise of the 

 heat of the whole body, in spite of the conservative arrangements, and 

 exposure to extreme cold compels a descent, we ought to expect that ex- 

 posure to more moderate degrees would, in like manner, produce an im- 

 pression. 



The old astrologers were therefore not altogether wrong when they af- 

 firmed the doctrine of planetary influences. The diurnal temperatures 

 of a locality, as dependent on the position of the sun, are expressed in 

 the system of man. The minimum of heat for the night, and the max- 

 imum for the day, find a correspondence in the decline of animal temper- 

 ature at the former, and its rise at the latter period. The experiments 

 of M. Chossat on birds submitted to absolute starvation showed that, 

 though in their normal state, at the commencement, the variation between 

 midnight and noon was only 1J, it gradually increased to 6, until at 



