THE EFFECT OF CLIMATE AND WEATHER 297 



the earth's surface would destroy most forms of life excep 

 near the poles. Some bacteria do indeed live in hot springs, 

 while dormant seeds and spores can endure still higher 

 temperatures provided the air be dry, but even in the 

 lowest organisms reproduction appears never to take place 

 unless the temperature is well below the boiling point of 

 water. As for man, the obvious limit is a temperature such 

 that the cooling mechanism of the sw^eat glands, skin, lungs 

 and circulation is no longer able to prevent the body tempera- 

 ture from rising permanently above normal. Experiments 

 indicate that even when healthy persons are at rest and 

 practically unclothed, a temperature of 93°f. in saturated air 

 is likely to cause the body temperature to rise as much as 5° in 

 two hours — a genuine fever which would presumably increase 

 and soon prove fatal if the atmospheric conditions were pro- 

 longed. In dry air a higher temperature can of course be en- 

 dured; a century and a half ago bold experimenters remained 

 uninjured in temperatures as high as 262°f. but even seven 

 minutes of such air raised the pulse from the normal of about 

 70 to 144 beats per minute. 



In Death Valley in southern California, a summer tempera- 

 ture ranging up to 120° or 130° each day for several months 

 is practically unendurable, even though the air is very dry. 

 A single season of such weather has been known to drive 

 people crazy, and almost no one can endure two summers. 

 A very strong woman might possibly bear healthy children 

 in such a place and the children might grow up, but it is 

 extremely doubtful whether any kind of human beings 

 could stand the summer heat if it continued all the year. 



As for the lower limit, many forms of life die promptly if 

 the temperature reaches freezing. Some fairly high forms 

 however, such as cold-blooded vertebrates like frogs, can 

 be frozen stiff and yet recover completely when melted. No 

 one knows exactly how low a temperature they can endure, 

 but so long as they are frozen and dormant, there can be no 

 reproduction and they are as good as dead. Hence for 

 plants and cold-blooded animals a freezing temperature is 

 practically the lower limit for the reproduction of the species. 

 Warmblooded animals can reproduce at lower temperatures, 

 and man seems able to withstand the lowest temperature of 



