THEORY OF DISEASE. 263 



amount of steam generated and its tension increase) 

 with the temperature in the fire-place, which de- 

 pends on the supply of coals and of air. There are 

 in these engines other arrangements, all intended 

 for regulation. When the tension of steam in the 

 boiler rises beyond a certain point, the passages for 

 admission of air close themselves ; the combustion 

 is retarded, the supply of force (of steam) is dimin- 

 ished. When the engine goes slower, more steam 

 is admitted to the cylinder, its tension diminishes, 

 the air passages are opened, and the cause of dis- 

 engagement of heat (or production of force) in- 

 creases. Another arrangement supplies the fire- 

 place incessantly with coals in proportion as they 

 are wanted. 



If we now lower the temperature at any part of 

 the boiler, the tension within is diminished ; this is 

 immediately seen in the regulators of force, which 

 act precisely as if we had removed from the boiler 

 a certain quantity of steam (force). The regulator 

 and the air passages open, and the machine supplies 

 itself with more coals. 



The body, in regard to the production of heat and 

 of force, acts just like one of these machines. With 

 the lowering of the external temperature, the respi- 

 rations become deeper and more frequent ; oxygen 

 is supplied in greater quantity and of greater den- 

 sity ; the change of matter is increased, and more 

 food must be supplied, if the temperature of the 

 body is to remain unchanged. 



