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A MANUAL OF PHYSIOLOGY 



because the muscles are at rest, but also to some extent 

 because the external stimuli that in waking life excite the 

 nerves of special sense are absent or ineffective. Even a 

 bright light is said to cause an increase in the amount of 

 carbon dioxide produced and of oxygen consumed ; but 

 recent experiments have cast doubt on the statement 

 (C. Ewald). The external temperature also has an influence. 

 In poikilothermal animals (such as the frog), the temperature 

 of which varies with that of the surrounding medium, the 

 production of carbon dioxide, on the whole, diminishes as 

 the external temperature falls, and increases as it rises. In 

 homoiothermal animals, that is, animals with constant blood 

 temperature, external cold increases the production of 

 carbon dioxide and the consumption of oxygen. But if the 

 connection of the nervous system with the striated muscles 

 has been cut out by curara, the warm-blooded animal behaves 

 like the cold-blooded (Pflliger and his pupils in guinea-pig 

 and rabbit). These interesting tacts will be returned to 

 under Animal Heat. 



Cold-blooded animals produce far less carbon dioxide, 

 and consume far less oxygen, per kilo of body-weight than 

 warm-blooded. 



The following table shows the relation between the body- 

 weight and the excretion of carbon dioxide in man : 



The next table illustrates the difference in the intensity of 

 metabolism in different kinds of animals, a difference, how- 

 ever, largely dependent upon relative size : 



