656 HANDBOOK OF PHYSIOLOGY. 



centres little or nothing is certainly known. It appears unlikely that 

 they possess the reflex functions of the spinal centres. 



As a contribution toward 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. Such a nerve is excellently illustrated by the sympa- 

 thetic 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 constructive metabolism. Stimulation of the nerve pro- 

 duces diminished activity, repair of tissue and building up. An exam- 

 ple 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 sub- 

 maxillary gland for example, if the sympathetic fibres be stimulated, a 

 katabolic effect is produced, and the materials of secretion are formed at 

 the expense of the protoplasm (this action in the case of the gland 

 Heidenhain calls trophic) ; if on the other hand the chorda tympani or 

 the secretory nerve be stimulated, two things happen, one being the 

 discharge of water and the materials of secretion from the gland cells, 

 and the other the building up or reconstruction of the protoplasm of the 

 cells. A part of this action at any rate is anabolic, and similar to the 

 action of inhibitory nerves. 



