Chap, v.] NUTRITION. 655 



which seem to shew that the central nervous system governs 

 the metabolic changes, the nutrition, not only of muscle and 

 gland, but of various other tissues in a deeper and more general 

 way than that of simply promoting (or hindering) contraction 

 or secretion. Thus as we have seen (§ 78) when the connection 

 between a muscle and the central nervous system is severed, 

 the muscle eventually wastes and loses its vitality ; when all 

 the nerves going to the sub-maxillary gland are severed, the 

 gland instead of being as in the normal condition intermittently 

 active and quiescent, pours forth a continuous " paralytic " 

 secretion and eventually degenerates and wastes. When in a 

 rabbit the fifth nerve is divided in the skull the loss of sensation 

 in those parts of the face of which it is the sensory nerve is 

 followed by nutritive changes. Very soon, within twenty-four 

 hours, the cornea becomes cloudy ; and this is the precursor of 

 an inflammation which may involve the whole eye and end in 

 its total disorganization. At the same time the nasal chambers 

 of the side operated on are inflamed, and very frequently ulcers 

 make their appearance on the lips and gums. And similar 

 results have been seen in other animals including man. If the 

 operation be conducted in a young animal, which subsequently 

 lives to maturity, the head may become bilaterally unsymmet- 

 rical, as shewn especially by the skull. Again division of both 

 vagus nerves is very apt to be followed by inflammation of 

 both lungs, by fatty degeneration of the heart, and so b}^ death. 

 In several of these instances the effect is a mixed one and 

 the problem complicated. Thus, in the case of division of the 

 fifth nerve, seeing how delicate a structure the eye is, and how 

 carefully it is protected by the mechanisms of the eyelids and 

 tears, it seems reasonable to suppose that the inflammation in 

 question might simply be the result of the irritation caused by 

 dust and contact with foreign bodies, to which the eye, no 

 longer guided and protected by sensations, these being destroyed 

 by the section of the nerve, became subject. In the same way 

 the ulcers on the lips and gums might be explained as injuries 

 inflicted by the teeth on those structures in their insensitive 

 condition. And some observers maintain that the inflammation 

 of the eye may be greatly lessened or altogether prevented if 

 the organ be carefully covered up and in all possible ways pro- 

 tected from the irritating influences of foreign bodies. Other 

 observers however have failed to prevent the inflammation in 

 spite of every care. So also the inflammation of the lungs 

 following upon division of both vagus nerves seems to be due 

 not to any direct nutritive action of the pulmonary branches of 

 the vagus on the pulmonary tissue, but to food accumulating 

 in the pharynx owing to the paralysis of the oesophagus and 

 larynx, and then passing into the air passages and so setting 

 up inflammation. Death in these cases is moreover often the 



