HEAT IN BREATHING. 197 



the sun so expand the air that the current to the fire 

 is greatly diminished, and stops altogether. We 

 hence see how very unskilfully many persons blow 

 the fire with bellows. They put the nose of the 

 bellows close to the fire, and thus drive the expanded 

 air upon all parts of the fire, except the little space 

 on which the blast acts; and the consequence is, 

 that that little portion is very rapidly and unprofitably 

 consumed, and the rest of the fire is not at all im- 

 proved ; whereas, if the bellows were kept farther 

 off they would blow a much more effective current 

 of air against the whole fire. The position of the 

 bellows should be sloping upward to the fire, because 

 then the air is of the proper quality ; whereas, if the 

 nose of the bellows slope downward, the "burnt 

 air" the nitrogen and the products of the fire are 

 blown against the fire, and tend to weaken it. 



The heat produced in breathing does not approach 

 nearly to that of flame or combustion, but still it is 

 considerable, though it is not easy to distinguish be- 

 tween it and the heat produced by circulation. 

 There is no reason to doubt that heat might be pro- 

 duced by resistance to circulation, and to that of 

 breathing, among other circulations, sufficient to 

 kindle and consume the body; for though all the 

 recorded instances of spontaneous or inward com- 

 bustion are not probably true, yet so many of them 

 are mentioned that they must have at least some 

 foundation. We know that when either the breath- 

 ing or the pulse of the blood is quickened, either by 

 exertion or by disease, the heat increases in propor- 

 tion ; so that while the temperature of health varies 

 from about ninety-five to one hundred degrees, a 

 diseased heat may be as great as one hundred and 

 thirty or one hundred and forty degrees. So also 

 when the breathing or the circulation is very lan- 

 guid the temperature sinks ; and in those faintings, 

 during which hardly any pulse or breathing is per- 

 ceptible, the body becomes exceedingly cold. 

 R2 



