290 BIOLOGICAL PROBLEMS 



and it is expressed in terms of mille-calories per square 

 centimetre per second. The wet Kata-thermometer 

 result will be at least 20 (it may reach 28 out-of-doors) 

 if the air is in a satisfactory state. 



This rate of loss of body heat by conduction and 

 convection is promoted by the movement of air past 

 the body more especially, of course, when the moving 

 air is cool. Fresh air refreshes by its rapid removal 

 of heat from the body; and the prime requirement of 

 ventilation is to keep the air relatively cool and in gentle 

 motion. The problem is one of maintaining air- 

 freshness rather than a\r-purity\ for the beneficial 

 results of fresh air are chiefly on the surface of the 

 body and not on the lungs. The bracing effect of the 

 ceaseless flow of sensory impressions resulting from 

 the movement of cool air over the skin is also of high 

 value in promoting our efficiency; we live on a higher 

 plane, and all our vital functions are "toned up". 

 Thus fresh air promotes the vigorous tone of the 

 nervous system; favours the circulation and the best 

 distribution of the blood in the system; more oxygen 

 and food are taken in, and metabolism is increased; 

 it tones up the system and makes us more vigorous 

 of brain and muscle; while warm, foul air relaxes and 

 enervates, and lowers our efficiency. It is not sur- 

 prising, therefore, that the sedentary worker in unduly 

 warm and insufficiently ventilated offices, work-rooms, 

 and sitting-rooms suffers a loss in bodily and mental 

 vigour. It is the penalty that he pays for his neglect 

 of fresh air and exercise. 



We must fight against the tendency to ik coddle", 

 to acquire that evil and unnatural hyper-sensitiveness 

 to cool air which is so much in evidence. . By ac- 

 customing ourselves to slight draughts, which are 



O t** -* 



inseparable from fresh-air conditions, we reduce 

 the risks from chills. This toleration can only be 



