284 Historical 



summarized, made during his ascent of Mont Blanc in 1864, also 

 attributes to fatigue alone the disturbances of circulation and 

 respiration; according to him, the drowsiness is due to cold, the 

 muscular fatigue to the cause indicated by Brachet, and the heavi- 

 ness of the lower muscles to the cause specified by Weber and von 

 Humboldt. 



But these not very original estimations have hardly any im- 

 portance beside the new and very ingenious theory advanced by 

 Dr. Lortet. 1 - 3 We have reported at length the observations made 

 with all the precision required by modern physiological research 

 by this learned physician during his ascent of Mont Blanc. The 

 discovery to which he gives most importance is the decrease of 

 the body temperature during the act of ascent. In his opinion, 

 this is the true cause of the symptoms experienced, and to explain 

 it, M. Lortet relies upon the elementary notions of the mechanical 

 theory of heat: 



In a state of rest and fasting, man burns the materials of his 

 blood, and the heat developed is wholly employed in maintaining his 

 temperature constant in the midst of atmospheric variations. On the 

 plain and during moderate mechanical work, the intensity of the 

 respiratory combustions, as M. Gavarret has shown, increases propor- 

 tionately to the expenditure of energy. There is a transformation of 

 heat into mechanical energy, but because of the density of the air 

 and the quantity of oxygen inspired, there is enough heat formed to 

 make up for this expenditure. 



In the mountains, especially at great altitudes and on very steep 

 snowy slopes, where the mechanical work of the ascent is great, an 

 enormous quantity of heat is needed to be transformed into muscular 

 energy. This expenditure of energy uses up more heat than the or- 

 ganism can furnish, hence the perceptible chilling of the body and the 

 frequent halts which must be made so that one can gain warmth. 

 Although the body is burning hot, although it is often covered with 

 perspiration, it becomes chilled during the ascent, because it uses up 

 too much heat and because the respiratory combustion cannot furnish 

 a sufficient quantity of it because the air lacks density; because of the 

 rarefaction of the air, at each inspiration less oxygen enters the lungs 

 at a great height than on the plain. (P. 33.) 



M. Lortet then shows, by a simple calculation, that while he is 

 ascending 1000 meters, a man weighing 75 kilograms would find 

 that the temperature of his body would drop 2.3°, if he furnished 

 no restorative heat. Hence he draws this conclusion that the drop 

 of 4° to 5°, which he noted in ascending to 3800 meters, is quite 

 natural and within the limits indicated by his theory: 



Let us take, for example, a human body weighing 75 kilograms, 

 and let us assume that during the ascent no combustion repairs the 



