512 



A MANUAL OF PHYSIOLOGY 



temperature. To reduce the temperature of a horse or an 

 elephant by i, a considerable quantity of heat must be lost, 

 while a very slight loss would suffice to cool a mouse by that 

 amount. Not only so, but the surface by which heat is lost 

 is greater in proportion to the mass of the body in small than 

 in large animals. The power of rapidly increasing the heat- 

 production to meet a sudden demand is, therefore, far more 

 important to the mouse than to the horse ; and the fact 

 (p. 479) that the metabolism of an animal varies approxi- 

 mately as its surface, and not as its mass,* is an illustration 

 of the nice adjustment by which heat-equilibrium is main- 

 tained. 



The following table, calculated by Rubner from the quantity of 

 tissue-proteid and fat consumed, shows the relative intensity of heat- 

 production in fasting dogs of different sizes : 



Rubner has found that animals abundantly fed do not show so 

 much change in the production of heat when the external tempera- 

 ture is varied as starving animals, perhaps because the thicker coat 

 of subcutaneous fat so steadies the rate at which heat is lost that it 

 becomes easy for the vaso-motor mechanism alone to hold the 

 balance between loss and production. In well-fed animals it is the 

 heat-loss which is chiefly affected, and it may be that this has some- 

 thing to do with the explanation of Loewy's results on man. 



Lorrain Smith has discovered the curious and interesting fact that 

 after removal of the thyroid glands (in cats), the heat-production, as 



* The relation between mass (M) and surface (S) in man is approxi- 



S 3/M 

 mately given by the equation JV = K, and the relation between sur- 



face, mass, length of body (L), and circumference of chest (C) just 

 above the nipples in the ' mean ' position of respiration, by the equation 

 . L4. C 



C - K'. M is expressed in grammes, S in square centi- 



metres, L and C in centimetres. K is a constant whose mean value is 

 12*3, and K' a constant whose mean value is 4-5 (Meeh). 



