WYMAN. — COOLING OF HOSPITALS. 485 



as those we now have, we might keep a ward at 70° with an outside 

 air of 90°, and a ventilation reduced to 40,000 cubic feet an hour, — 

 one third of our winter supply, or one tenth of our summer supply. 

 But we have no reliable experiments to confirm this computation. Our 

 own experiments have shown that this previous cooling of the air is an 

 expensive and uncertain process, and would lessen the evaporation 

 upon which, as we shall see further on, we principally depend for 

 cooliug, and, what is more important, would probably not be hygienic. 

 No further experiments were made as to cooliug the air before its 

 entrance into the ward. 



Our first experiment showed clearly enough the advantage of a 

 large supply of fresh and slightly cooled air ; but it is not so clear 

 how much was due to the temperature of the air, and how much to 

 the rapid evaporation caused by its velocity and dryness. But as the 

 comfort of the sick continued the same after the rise of temperature 

 of the cooling apparatus and the shutting off of the cold water, it is 

 probable that it was due more to the velocity and drying qualities of 

 the air acting upon the patients themselves, than to any change of 

 temperature in the ward generally, which, as we have already said, 

 differed but little from that of the open air. This is a point of the 

 first importance. 



The most effective way of losing heat is that last mentioned, that is, 

 by evaporation. It is Nature's great consumer of heat. Evaporation 

 increases with the temperature of the air, with its dryness, and with 

 its velocity. Common observation teaches how rapidly wet clothing 

 and muddy roads dry in windy weather. If we are exposed to a warm 

 dry air, especially if it is in motion, we may feel cool, or even cold, 

 because of the rapid evaporation from the skin. In the heats of 

 summer the relative dryness of the air is of more importance to our 

 comfort than its temperature. The thermometer and our sensations do 

 not correspond. It is evaporation increased by the air put in motion 

 by his punkah that enables the Englishman to bear the heats of India 

 and keep his blood at its normal temperature. 



Pettenkofer calculates that in twenty-four hours we lose heat, by 

 respiration alone, as follows : — 



In dry air at 32° F. 



« u 86° 



A difference of about 

 In air completely humid at 32° 



<.i ii a (; 86° 



A difference of nearly 



