200 NUTRITIONAL PHYSIOLOGY 



than cooled as it approaches the surface. The metabolism 

 will continue unabated. The body is thus exposed to 

 warming from without, while it does not cease to heat itself 

 from within. How can it escape a steady rise of its in- 

 ternal temperature leading to prostration and death? 

 Benjamin Franklin answered this question when he pointed 

 out that the sole resource of the organism in such a situa- 

 tion must be its power to evaporate water. To dispose of 

 100 Calories in an hour by evaporation alone demands the 

 secretion of about 200 grams of water in the same time, an 

 amount which can readily be produced. 



When the air is warm the humidity has much to do with 

 human power to endure the condition. If there is full 

 saturation and a temperature as high as that of the blood 

 the heat of metabolism will be pent in the body and heat- 

 stroke is inevitable if there is not a prompt relief; 100 Calor- 

 ies added to the average human body in an hour will raise 

 its temperature by nearly 4 F. A second hour of such 

 an upgrade could hardly be survived. Men may live and 

 work for several hours on a stretch in dry air with the tem- 

 perature around them as high as 130 F., but they cannot 

 be active in saturated air at 90 F. The first of these 

 conditions is realized in the stoke-holds of ocean steamers ; 

 the second, in certain deep mines. Everyone knows that 

 the most trying weather we have to put up with is not 

 that which makes the record for the mercury, but those 

 days which are less warm, but which we describe as muggy 

 or sticky. We are acceding to a correct instinct when we 

 are relaxed and indolent under such circumstances. 



We may now return to the starting-point and submit our 

 imaginary victim to temperatures lower than 68 F. If 

 he is taken to a room where the thermometer is at 60 F. 

 he will probably feel chilly. We are affected more by a 

 slight change in the vicinity of 65 F. than in any other 

 part of the scale. The fact is, apparently, that when the 

 external temperature is cut down from 68 to 60 F. the 

 skin temperature, on which our sensation depends, is re- 

 duced by a good deal more than 8 degrees. This is due to 



