632 HANDBOOK OF PHYSIOLOGY. 



than in other salamanders in whom the spinal cord was left uninjured 

 above the point at which the tail was amputated. Illustrations of the 

 same kind are furnished by the several cases in which division or de- 

 struction of the trunk of the trigeminal nerve has been followed by 

 incomplete and morbid nutrition of the corresponding side of the face; 

 ulceration of the cornea being often directly or indirectly one of the 

 consequences of such imperfect nutrition. Part of the wasting and slow 

 degeneration of tissue in paralyzed limbs is probably referable also to the 

 withdrawal of nervous influence from them; though, perhaps, more is 

 due to the want of use of the tissues. 



Undue irritation of the trunks of nerves, as well as their division or 

 destruction, is sometimes followed by defective or morbid nutrition. To 

 this may be referred the cases in which ulceration of the parts supplied 

 by the irritated nerves occurs frequently, and continues so long as the 

 irritation lasts. 



So many and varied facts leave little doubt that the nervous system 

 exercises an influence over nutrition as over other organic processes; and 

 they cannot be easily explained by supposing that the changes in the 

 nutritive processes are only due to the variations in the size of the blood- 

 vessels supplying the affected parts, although this is, doubtless, one im- 

 portant element in producing the result. 



As a contribution towards the explanation of the nervous mechanism 

 of nutrition comes in Gaskell's theory of katabolic and anabolic nerves. 

 He supposes that every tissue is supplied with two sets of nerves, the- 

 former of which corresponds with the motor nerve, the viscero-motor, 

 and the cardio-augmentor, by the stimulation of which an increase of the- 

 metabolism takes place, and which is followed by exhaustion. It may 

 be accompanied either by contraction of a muscle or by an increase of 

 contraction. Sujch a nerve is excellently illustrated by the sympathetic 

 augmentor or accelerator nerve of the heart, on stimulation of which an 

 increase in the force and frequency of the heart takes place, followed 

 after a time by exhaustion. A katabolic nerve stimulates the destructive- 

 metabolism which is always going on in a tissue. The anabolic nerve is 

 the exact opposite of the katabolic nerve in function. It subserves con- 

 structive metabolism. Stimulation of the nerve produces diminished 

 activity, repair of tissue, and building up. An example of this kind of 

 nerve is seen in the cardiac vagus, stimulation of which produces 

 inhibition. Inhibition must generally be looked upon as an anabolic 

 process. 



It will be seen that the results of stimulation of the nerves to the 

 salivary glands, discussed in a former chapter, appear to support the- 

 theory that the processes of constructive and destructive metabolism are 

 under the control of separate nerve fibres. In the case of the submaxil- 

 lary gland, for example, if the sympathetic fibres be stimulated, a kata- 



