1224 



PHYSIOLOGY 



contraction. The effect of muscular activity on the total output of energy 

 of the body is well represented in the Table given on p. 684. 



It is probable that, in relation to their size at any rate, the glands are 

 still more effective as heat producers. The liver and the blood flowing 

 from the liver have been stated to present a higher temperature than any 

 other part of the body. On the other hand, the nervous system, although 

 dependent on a constant supply of oxygen for its activities, does not appear 

 to be the seat of extensive metabolic changes, nor does the heat produced in 

 this system play any great part in maintaining the temperature of the body. 



The skeletal muscles are controlled by the central nervous system; if 

 separated from their centres in the cord they become flaccid and rapidly 

 atrophy. The heat production in the muscles is therefore also dependent on 

 their connection with the central nervous system. If this connection be 

 severed either by curare or section of the cord, or if the reflex play of impulses 

 on the muscles be abolished by anaesthetics, .the animal will react like a cold- 

 blooded animal. The total metabolism of the body and the total production 

 of heat sink to a minimum, and are diminished by application of cold, or 

 increased by application of warmth, to the surface of the body. On the 

 other hand, in the intact animal changes of temperature in the environment 

 provoke, reflexly by their action on the muscles, changes in the opposite 

 direction . Thus exposure to cold increases and to heat diminishes muscular 

 metabolism and the heat production of the body. 



The effects of variations in the external temperature on the metabolism 

 of warm-blooded animals are well shown in the experiment, from which 

 the following Tables are taken, on the C0 2 output in the ornithorhynchus 

 and in the rabbit (Martin) : 



1. ORNITHORHYNCHUS. WEIGHT, 693 GRM. ; SURFACE, 876 SQ. CENTTMS. 



2. RABBIT. WEIGHT, 750 GRM. 



