250 THEORY OF DISEASE. 



eased part ; that if the ice be removed before the com- 

 pletion of the metamorphosis, the temperature again 

 rises ; that far more heat is removed by means of ice 

 than if we were to surround the head with a bad con- 

 ductor of heat. There has obviously been liberated in 

 an equal time a far larger amount of heat than in the 

 state of health ; and this is only rendered possible by 

 an increased supply of oxygen, which must have deter- 

 mined a more rapid change of matter. 



The self-regulating steam-engines, in which, to pro- 

 duce a uniform motion, the human intellect has shown 

 the most admirable acuteness and sagacity, furnish no 

 unapt image of what occurs in the animal body. 



Every one knows, that in the tube which conveys the 

 steam to the cylinder where the piston-rod is to be 

 raised, a stop-cock of peculiar construction is placed, 

 through which all the steam must pass. By an arrange- 

 ment connected with the regulating wheel, this stop- 

 cock opens when the wheel moves slower, and closes 

 more or less completely when the wheel moves faster 

 than is required for a uniform motion. When it opens, 

 more steam is admitted (more force), and the motion of 

 the machine is accelerated. When it shuts, the steam 

 is more or less cut off, the force acting on the piston- 

 rod diminishes, the tension of the steam increases, and 

 this tension is accumulated for subsequent use. The 

 tension of the vapor, or the force, so to speak, is pro- 

 duced by the change of matter, by the combustion 

 of coals in the fire-place. The force increases (the 



