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XVII. Animal Thermostat. By Lord Kelvin *. 



THERMOSTAT is an apparatus, or instrument, for 

 automatically maintaining a constant temperature in 

 a space, or in a piece of solid or fluid matter with varying 

 temperatures in the surrounding matter. 



Where and of what character is the thermostat by which 

 the temperature of the human body is kept at about 98°*4 

 Fahrenheit? It has long been known that the source of 

 heat drawn upon by this thermostat is the combination of 

 food with oxygen, when the surrounding temperature is below 

 that of the body. The discovery worked out by Lavoisier, 

 Laplace, and Magnus still holds good, that the place of the 

 combination is chiefly in tissues surrounding minute tubes 

 through which blood circulates through all parts of the body, 

 and not mainly in the place where the furnace is stoked by 

 the introduction of food, in the shape of chyle, into the circu- 

 lation, nor in the lungs where oxygen is absorbed into the 

 blood. It is possible, however, that the controlling mechanism 

 by which the temperature is kept to 98°'4 may be in the 

 central parts, about, or in, the pumping station (the heart) ; 

 but it may seem more probable that it is directly effective in 

 the tissues or small blood-vessels in which the combination of 

 oxygen with food takes place. 



But how does the thermostat act when the surrounding 

 temperature is anything above 98°'4 and the atmosphere 

 saturated with moisture so that perspiration could not evaporate 

 from the surface ? I£ the breath goes out at the temperature 

 of the body and contains carbonic acid, what becomes of the 

 heat of combustion of the carbon thus taken from the food ? 

 It seems as if a large surplus of heat must somehow be carried 

 out by the breath : because heat is being conducted in from 

 without across the skin all over the body; and the food and 

 drink we may suppose to be at the surrounding temperature 

 when taken into the body. 



Much is wanted in the way of experiment and observation 

 to test the average temperature of healthy persons living in a 

 thoroughly moist atmosphere at temperatures considerably 

 above 98°*4: and to find how much, if at all, it is above 98°*4. 

 Experiments might also, safely I believe, be tried on healthy 

 persons by keeping them for considerable times in baths at 

 106° Fahr. with surrounding atmosphere at the same tempe- 

 rature and thoroughly saturated with vapour of water. The 



* Communicated by the Author ; having been read before Sectio n A 

 of the British Association at Belfast. 



