THERMAL PHENOMENA OF THE BODY 211 



work and the efficiency of digestion are examples we have 

 already studied and more could easily be cited of func- 

 tions which, important as they are, are subordinated, even 

 sacrificed, to prevent a marked rise or fall in the temperature 

 of the blood. 



To such an extent is the nervous system as a whole 

 adapted to maintain the constant temperature, that the failure 

 to do this, as shown by the presence of fever or by the even 

 more serious subnormal temperature, becomes one of the 

 most important indications that something has gone wrong. 

 We know already how the nervous system intervenes in 

 every function of our lives, and how the well-being of the 

 body as a whole depends upon the adjustments which it 

 brings about. It is for these reasons that, when it is no 

 longer able to exercise that firm control of the constant tem- 

 perature which is one of its most characteristic features in 

 health, the physician's orders usually are to " go to bed and 

 be perfectly quiet." The body is then in no condition to 

 make demands on the nervous system for action ; and a per- 

 son who refuses to heed the plain warning which his tempera- 

 ture holds out has nothing but his own foolishness to blame 

 if he suffers serious consequences. 



26. Definitions. Those not familiar with the exact meaning 

 of the terms " conduction," " convection," and " radiation " 

 will find the following helpful. 



Conduction. Whenever heat is transferred directly from one 

 mass of matter to another with which it is in contact, such 

 transfer is known as conduction. A good example is the heating 

 of a poker in a fire ; the heat of burning coal is communicated 

 directly to the outer particles of iron and then from one particle 

 of the iron to another. The particles of iron do not move up and 

 down the length of the poker ; each one simply passes on to the 

 next the heat it has received, and finally those of the handle com- 

 municate their heat to the hand. All transfer of heat along solid 

 objects, or from one mass of matter to another with which it is in 

 immediate contact, is by means of conduction. 



