382 SCIENCE PROGRESS. 



constant from io° up to 22*5° on warming, and diminished 

 only very slightly over similar temperature intervals on 

 cooling. In the cockroach alone of the animals examined, 

 did the carbonic acid output increase and decrease uniformly 

 with increase and decrease of temperature. 



To what is this want of dependence of metabolism on 

 temperature due? It must obviously be ascribed either to 

 a direct control of the central nervous system over the re- 

 spiratory activity of the tissues, or to the tissues being them- 

 selves so constituted that their metabolism is affected by 

 temperature in this curious and irregular manner. This 

 second supposition appears on the face of it highly im- 

 probable, and that it is actually incorrect was experiment- 

 ally proved. Thus it was found that if a transverse section 

 were made in the medulla of the frog or toad, at the level 

 of its lower border, the carbonic acid output now varied uni- 

 formly with the temperature and showed no intervals of 

 constancy. If, however, the transverse section were made 

 at the level of the upper border of the medulla, the relation 

 of carbonic acid output to temperature was as a rule the 

 same as in intact frogs, though occasionally irregular results 

 were obtained. It appears therefore that there is a definite 

 centre situated somewhere in the region of the medulla, and 

 that this centre is able to send out impulses to the various 

 tissues of the body, and so control their metabolism. Pro- 

 bably the muscles are the tissues chiefly concerned in the 

 maintenance of this metabolism, and it might be thought 

 that it is maintained through the agency of the ordinary 

 motor nerves which are concerned in muscular contractions. 

 This does not seem to be the case, however, as it was found 

 that if doses of curare were given to frogs sufficient to 

 paralyse all voluntary and reflex muscular movements, the 

 carbonic acid output still varied irregularly with the tempera- 

 ture. It was only when excessive doses of the drug were 

 administered that the one varied regularly with the other. 



We see, therefore, that in almost all the cold-blooded 

 animals examined, there exist intervals of temperature over 

 which, through the agency of a nervous regulating mechan- 

 ism, the metabolism remains more or less constant. When 



