RELATIONS OF THE AIR TO OUR CLOTHING. 659 



morphosis of tissue, whether this increase was the consequence of 

 increased nutrition, or of muscular exertion. We have experimented 

 upon men at rest and at work, and we have found that on a day of 

 rest they usually evaporated through lungs and skin about two 

 pounds only during twenty-four hours, and on a day of hard work 4 

 pounds of water. In the first instance, about 2,016 caloric units, in 

 the second, 4,480 had to leave the body in consequence of evaporation. 



This explains to you how it can be that even with the hardest 

 work our blood will not become warmer, but sometimes even cooler. 

 The last observation has been made quite recently in mountaineering 

 expeditions. Prof. Lortet, of Lyons, found, when he made an ascent 

 of Mont Blanc, that the temperature in his mouth and armpit was 

 less than normal, and became normal only when he was at rest. On 

 such high mountains the lessened pressure of the atmosphere favors 

 the peripheric circulation, there is a rush of water to the surface, 

 and its evaporation takes place more readily, and increases with the 

 altitude. At great heights persons in a balloon constantly complain 

 of great dryness in the mouth. 



Profs. Voit, Recknagel, and myself, are just now occupied in 

 investigating the economy of animal heat, and we have found that 

 after six hours' hard work the person leaves the apparatus in a cooler 

 condition than when he went in, or after he had been at rest in the 

 apparatus for the same space of time. Of course, the ventilation of 

 the apparatus must work well, and send per hour about 11,100 gallons 

 or 1,800 cubic feet of air through the chamber, else less water and less 

 heat depart by evaporation. 



You see what powerful means of cooling our body we have in the 

 increase of our peripheric circulation, and consequent evaporation, at 

 a time when the other routes are not open sufficiently but you see 

 also how dangerous this means can become, if it is employed at a 

 time when considerable quantities of heat depart on the other routes. 

 If, heated and damp, you enter suddenly a cold space, where radia- 

 tion increases at once, and a good deal of heat is also yielded by con- 

 duction to the cold air, you are in great danger of contracting an 

 illness by the abnormal losses of heat, and the violent and sudden 

 changes in the circulation. But if you undergo such changes slowly 

 and gently, the three routes open themselves harmoniously. Our or- 

 ganism is a faithful and clever servant, who helps himself and his 

 master-, provided he is not hurried and ill-treated. When I come to 

 speak of ventilation, I shall not forget to tell you of currents of air, 

 called draughts. 



The third route, that of conduction, by which we give up heat to 

 the air, is also of great importance, and must in some circumstances 

 replace the two others to a considerable degree. As long as our body 

 is warmer than the surrounding air, this air gets warmer at every 

 point of contact with our body, but at the same time lighter, and as 



