656 THE POPULAR SCIENCE MONTHLY. 



that continuous work, which goes on day and night a never-ceasing 

 bellows-blowing, by which the organ of our life is kept in play. Of 

 course, the quantity of air flowing round the surface of the human 

 body is much greater thanr that. Do not object, that air is something 

 so light that it need not be taken into account. It has some weight ; 

 water, certainly, is 770 times heavier, but our daily 2,000 gallons have 

 for all that a weight of 25 pounds avoirdupois. Still, as it is not my 

 intention to dwell here upon the subject of our oxygen-alimentation, 

 I will to-day consider only the second use we make of the air, the cool- 

 ing of our working machine. 



You all know that life is bound up with chemical processes, kept 

 in continual activity through the ingestion of solid and liquid food, 

 and of oxygen from the ah*. One of the conditions for the normal per- 

 formance of these processes is a definite temperature, above and below 

 which they (although not brought to a standstill) go on differently 

 they leave off performing the functions of normal life they lead to dis- 

 ease or death. With man this uniform temperature of his organs is 

 one of the most essential conditions of his life. The blood of the negro 

 living in the torrid zone of the equator is not by one-fifth degree warmer 

 than that of the Esquimaux in the highest north at the coldest time 

 of the year it is always 99| Fahr. The extremes of temperature 

 under which human life exists are 95 to 104 Fain*, in the tropics, 

 and 57 to 84 under freezing-point in the polar regions. There are 

 even differences of 72 in the mean monthly temperatures of some 

 countries, and yet the organs of man are everywhere of the same tem- 

 perature. 



By what means is man enabled to meet such colossal differences ? 

 What are his weapons for sustaining this gigantic struggle ? 



Let us look a little nearer into the absolute quantities of heat the 

 living organism has to manage. The chemical processes going on in 

 an adult person, within the space of twenty-four hours, produce about 

 12,000 caloric units. By caloric unit natural philoso]}hy designates that 

 quantity of heat which is necessary to raise the temperature of one 

 pound avoirdupois of water by one degree of Fahrenheit. 1 By the 

 heat produced by one person during one day about GC0 gallons of 

 water could be made warmer by nearly two degrees, or 7^ gallons 

 could be heated from freezing to boiling point, from 32 to 212 Fahr. 



Under certain conditions man produces more or less heat ; for in- 

 stance, according to the quantity of food he takes, or the degree of 

 muscular exertion he undergoes, such deviations from the mean 

 amounting at times to 50 per cent, of the whole quantity ; but it is 

 always the task of the body, and a strict condition for the mainte- 

 nance of health, to keep the heat of the blood substantially the same, 

 or at least within two degrees. 



We have to look upon ourselves as warm and humid bodies placed 

 1 Rankine's caloric units are used by the translator. 



