452 COMPARATIVE PHySIOLOGY. 



itself is to be sought for in the principle of natural selection. 

 It was open to certain organisms, we may assume, either to 

 adapt to a temperature much below that of their blood, or to 

 hibernate; failing to make either adaptation would result in 

 death ; and gradually, no doubt, involving the death of num- 

 berless individuals or species, the resisting power attained the 

 marvelous degree that we are constantly witnessing in all 

 homoiotherm.ers. 



The daily variations of the bodily temperature in homoio- 

 thermers is a beautiful example of the law of rhythm evident 

 in the metabolism. Hibernation is another such. While these 

 are clear cases, it is without doubt true that, did we but know 

 more of the subject, a host of examples of the operation of this 

 law might be instanced. 



We can but touch on these subjects enough to show that 

 they deserve an attention not as yet bestowed on them ; and to 

 the thoughtful it will be evident that their influence on prac- 

 tical life might be made very great were they but rightly ap- 

 prehended. 



THE INFLUENCE OP THE NERVOUS SYSTEM ON 

 METABOLISM (NUTRITION). 



This subject is of the utmost importance, and has not re- 

 ceived the attention hitherto, in works on physiology, to which 

 we believe it is entitled, so that we must discuss it at some 

 length. 



We may first mention a number of facts on which to base 

 conclusions: 1. Section of the nerves of bones is said to be fol- 

 lowed by a diminution of their constituents, indicating an 

 alteration in their metabolism. 3. Section of the nerves sup- 

 plying a cock's comb interferes with the growth of that ap- 

 pendage. 3. Section of the spermatic nerves is followed by de- 

 generation of the testicle. 4. After injury to a nerve or its 

 center in the brain or spinal cord, certain afEections of the 

 skin may appear in regions corresponding to the distribution 

 of that nerve ; thus, herpes zoster is an eruption that follows 

 frequently the distribution of the intercostal nerve. 5. When 

 the motor cells of the anterior horn of the spinal cord or cer- 

 tain cells in the pons, medulla, or crus cerebri are disordered, 

 there is a form of muscular atrophy which has been termed 

 " active," inasmuch as the muscle does not waste merely, but 



