ANIMAL HEAT 



593 



The following table shows how close is the agreement in the heat- 

 production per unit of surface calculated by the formula for animals 

 of different species and very different body-weight. 



Horse 

 Man - 

 Dog - 

 Rabbit 

 Fowl - 

 Mouse 



The next table, calculated by Rubner from the quantity of 

 tissue-protein and fat consumed, gives 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 (p. 591). 



Lorrain Smith discovered the interesting fact that after removal 

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

 by the amount of carbon dioxide given off, is more sensitive to 

 changes of external temperature than in the normal animal. 



But it must not be imagined that the production of heat can be 

 increased indefinitely to meet an increased heat-loss. The organism 

 can make considerable efforts to protect itself, but the loss of heat 

 may easily become so great that the increase of metabolism fails to 

 keep pace with it. The internal temperature then falls, and if the 

 fall be not checked, the animal dies. A mammal, when cooled arti- 

 ficially to the temperature of an ordinary room (15 to 20 C.), does 

 not recover of itself, but may be revived by the employment of arti- 

 ficial respiration and hot baths, even when the rectal temperature 

 has sunk to 5 to 10 C. If the skin of a rabbit be varnished, and 



38 



