THEORY OF DISEASE. 251 



amount of steam generated, and its tension increase) 

 with the temperature in the fire-place, which depends 

 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 diminished. When the engine goes 

 slower, more steam is admitted to the cylinder, its ten- 

 sion diminishes, the air passages are opened, and the 

 cause of disengagement of heat (or production of force) 

 increases. 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 immedi- 

 ately seen in the regulators of force, which act precise- 

 ly as if we had removed from the boiler a certain quan- 

 tity of steam (force). The regulator and the air pas- 

 sages 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 respira- 

 tions become deeper and more frequent ; oxygen is 

 supplied in greater quantity and of greater density ; the 

 change of matter is increased, and more food must be 

 supplied, if the temperature of the body is to remain 

 unchanged. 



