OX THE ORGANIC FUNCTIONS. 473 



625. That many of the Organic Functions, however, are directly influenced 

 by the Nervous System, is a matter which does not admit of dispute ; and 

 this influence, exerted sometimes in exciting, sometimes in checking, and 

 sometimes in otherwise modifying them, may well be compared to that, 

 which the hand and heel of the rider have upon his horse, or which the en- 

 gine-driver exerts over a locomotive. It is most remarkably manifested in the 

 result of severe injury of the Nervous centres, such as concussion of the 

 Brain, or of the Solar plexus ( 580) ; for this does not merely produce a sus- 

 pension of the respiratory and other movements, which minister to the or- 

 ganic functions, and hence a gradual stagnation of the latter, but a sudden 

 and complete cessation of the whole train of action ; which cannot be attri- 

 buted to any other cause than a positive depressing influence of some kind, 

 propagated through the Nervous System. It will hereafter appear ( 701), 

 that in such cases even the vitality of the Blood is often affected; the usual 

 coagulation not taking place after death, so long, at least, as the blood remains 

 within the vessels. A similar general depression may result from Mental 

 Emotion, operating through the same channel ; but this more commonly 

 has rather a local action, or operates more gradually. The influence of the 

 Nervous System is often especially exerted, in giving temporary excitement 

 to a Secreting process ; which need not be kept in constant activity, or of 

 which circumstances may occasionally require an increase. This is the 

 case, for example, in regard to the secretions connected with the process of 

 digestion, the Saliva, Gastric fluid, Bile, Pancreatic fluid, &c. ; all of these 

 being excited by the contact of the substances on which they act, with the 

 surfaces on which their respective ducts open. The secretion of Milk, again, 

 in a nursing female, may be excited by irritation of the nipple ; and the de- 

 termination of blood to the Mammae during pregnancy, must be due to in- 

 creased action in the part, excited by the changes occurring in the Uterus, 

 which can scarcely operate otherwise than through the Nervous System. No 

 other channel of influence can be well imagined for most of these operations, 

 than the Sympathetic system of Nerves ; since the organs in question are for 

 the most part supplied by it. There is an apparent exception, however, in 

 the case of the Salivary and Lachrymal glands, which are supplied by the 

 Fifth pair ; but this nerve contains so many organic filaments, and is so inti- 

 mately connected with the Sympathetic, as evidently to supply (in the head) 

 the place of a separate ganglionic system. It is by Nervous influence, that 

 the mucous secretion covering the membranes is caused to be regularly formed 

 for their protection ; for it is shown, by pathological facts, that, when this 

 influence is interrupted, and the secretion is no longer supplied, the membrane 

 losing its protection, is irritated by the air or the fluids with which it may be 

 in contact, and passes into an inflammatory condition. This is the explana- 

 tion of the fact, which has been well ascertained, that the Eye is liable to 

 suppurate when the Fifth pair has been divided ; and that the mucous Mem- 

 brane of the bladder becomes diseased in Paraplegia. 



626. The influence of particular conditions of the mind, in exciting various 

 Secretions, is a matter of daily experience. The flow of Saliva, for exam- 

 ple, is stimulated by the idea of food, especially that of a savoury character. 

 The Lachrymal secretion, again, which is continually being formed to a small 

 extent, for the purpose of bathing the surface of the eye, is poured out in 

 great abundance under the moderate excitement of the emotions, either o4' 

 joy, tenderness, or grief. It is checked, however, by violent emotions ; hence 

 in intense grief the tears do not flow. It is a well-known proof of moderated 

 sorrow, when this takes place ; tears, however, do not bring relief, as is com- 

 monly believed, but they indicate that it has been brought. Violent emotion 

 may also suspend the Salivary secretion ; as is shown by the well-known test. 



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