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THE PHYSIOLOGICAL PRINCIPLES OF VENTILATION 763 



ing application to the skin of cold towels, or while cold air from a fan 

 was allowed to play on it. A rise in temperature would indicate that the 

 part had become more vascular, and a fall, the contrary. That this in- 

 terpretation was the correct one was confirmed by direct inspection of 

 the degree of flushing (redness). It was found that chilling the body 

 surface immediately caused a fall in the temperature of the mucous mem- 

 branes which could not be accounted for by any accompanying change 

 in blood pressure, or, entirely at least, by changes in respiration or by 

 lowering of the temperature of the blood. The conclusions are "that chill- 

 ing of the body surface causes reflex vasoconstriction and ischemia in 

 the mucous membranes of the palate, f aucial tonsils, oropharynx and naso- 

 pharynx. ' ' 



The Methods for Determining the Healthfulness of Air. Although the 

 present review does not venture to discuss the methods that are employed 

 for the measurement of the various physical properties which have to 

 be considered in gauging its influence on health, or the engineering 

 problem of how ideal conditions may be maintained, it may not be out 

 of place to mention, in connection with the former of these, that the 

 physical property to which most attention should be devoted is the cool- 

 ing power. This can not be done by reading an ordinary thermometer, 

 for this instrument only registers the temperature of the piece of wood 

 and of the wall against which it is hung. It registers the same whether 

 the air is dry or moist, or whether it is stagnant or moving. Somewhat 

 more information regarding cooling power is afforded by readings of a 

 wet-bulb thermometer, an instrument in which the bulb is kept constantly 

 moist, so that evaporation occurs from it. This evaporation tends to cool 

 the thermometer, in proportion to its rate, and since this is dependent 

 mainly on the degree to which the air can take up more moisture, we can 

 tell by the use of a formula or tables the relative degree of humidity of 

 the air. Still this does not tell us the real degree of cooling which the 

 atmosphere can bring about. It does not adequately register the cooling 

 which is dependent upon the movement in the air, the so-called convec- 

 tion currents. To afford this information Leonard Hill has invented what 

 he calls the Kata thermometer, by which the rate of cooling is directly 

 measured. The instrument consists of an alcohol thermometer with a rel- 

 atively large bulb, and with the scale registering between 105 F and 90 

 F. It is placed in warm water at about the former temperature, and is 

 then removed, and the time required for the temperature to fall from 

 100 F. to 95 F. is measured by means of a stop watch. This time di- 

 vided by a factor determined for each instrument, and written on the 

 stem, gives the actual amount of heat in millicalories per square centi- 

 meter per second which would be given off from, say the surface of the 

 human body, under similar environmental conditions. Hill and his as- 



