562 Mr. Leonard Hill [Jan. 28, 



Dealing with the principles of ventilation, the lecturer pointed 

 out that attention had been wrongly focused on the chemical purity 

 of the air. The air in our rooms was never vitiated by the chemical 

 products of respiration to such an extent as to have the least physio- 

 logical effect. The two things that mattered most were : (1) bacterial 

 purity — prevention of spread of infection by saliva spray from 

 carriers of disease, most difficult to prevent when people crowd so 

 closely together in trains, lifts, meeting-houses, etc., and talk, cougb, 

 and sneeze at each other ; (2) the maintenance of a proper and not 

 monotonous rate of cooling of the skin. Of importance, too, was the 

 freedom of the air from dust and irritating and unpleasant products 

 of combustion, smoke, petrol fumes, and smells that depress our 

 feelings. The methods in vogue of warming and ventilation too often 

 gave us monotonous windless atmospheres which did not cool and 

 stimulate the skin. The ideal conditions out of doors were radiant 

 heat of the sun and a cooling variable breeze. Indoors we wanted a 

 source of radiant heat and cool air, gently wafted first this way and 

 then that, to prevent monotony or unpleasant draught. The open 

 fire, or the modern gas fire, gave us radiant heat, and reversing fans 

 could be used to give changing wafts of air. Hot-air plenum 

 systems gave entirely the wrong conditions. In the House of 

 Commons the members' feet were made cold and their heads too 

 warm by the air impelled up through the floor gratings, a con- 

 dition which leads to congestion and swelling of the mucous membrane 

 of the nose. The lecturer demonstrated the surface temperatures of 

 the skin and clothes, and how these were affected by radiant heat and 

 wind, and pointed out the protection afforded the negro by the black 

 pigment in his skin to the tropical sun. The black man's pigment 

 absorbs the sunlight on the surface of the skin, converts it into heat 

 which stimulates the transudation of water, so the heat is sweated off. 

 In the white man the sunlight penetrates and warms the deeper layers 

 of the skin and the blood therein. Thus the white man has to 

 shield himself with clothes. These surround him with stationary 

 humid warm air, preventing the cooling effect of wind. Thus the 

 white man cannot do field labour in the tropics, and must be a 

 burden on the black man's labour. AYhite clothes reflect and scatter 

 the sun's rays, while black and dark colours absorb them and convert 

 them to heat rays ; therefore we need to wear white in the sun's 

 heat, and black or dark colours in cold climates. The lecturer next 

 demonstrated his Kata- thermometer, an instrument devised for 

 measuring the cooling power of the skin surface at body tempera- 

 ture. This, a large-bulbed spirit thermometer (of standard shape 

 and size), is heated above 110' F. and then allowed to cool, and the 

 rate of cooling from 100° to 95° F. measured with a stop-watch.* 



* A factor is determined for each instrument which allows the readings to 

 be converted into mille-calories of heat loss per sq. cm. per sec. 



