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830 INFLUENCE OF NERVES ON NUTRITION. [BOOK n. 



the behaviour of a muscle or a gland as far as contraction and 

 secretion are concerned is, within certain limits, under experimental 

 control. But there are certain phenomena, seen chiefly in the course 

 of disease, and lying, to a very small extent only, within the control 

 of experiment, which seem to shew that the central nervous system 

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

 * s 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 ( 83) 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 be- 

 come bilaterally unsymmetrical, 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 by 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 protected from the irritating influences of foreign 

 bodies. Other observers however have failed to prevent the in- 

 flammation 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 



