846 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



paroxysm, among which may be specially reckoned all such as promote the 

 healthful performance of the menstrual function ; and, lastly, all those which act 

 beneficially on the Mind, diverting or repressing painful emotions, or substitut- 

 ing pleasurable feelings in their place, and strengthening the general control of 

 the Will. 



xvu. The foregoing are the chief Convulsive diseases in which the Spinal 

 centres generally are involved ; but there are many spasmodic affections of a 

 more limited character, which are traceable to a morbid affection of some parti- 

 cular division of the Spinal Axis. Thus in the various forms of Spasmodic 

 Asthma, the Medulla Oblongata would seem to be alone involved ; the attacks 

 of this disorder usually resulting from some internal irritation, either in the air- 

 passages themselves, or in the digestive system, producing a reflex contraction 

 of the muscular fibres of the bronchial tubes. In the purely spasmodic stage of 

 Hooping- Cough, again, which frequently persists long after all inflammatory 

 symptoms have subsided, we have another example of spasmodic action limited 

 to the respiratory centres ; and here we have distinct evidence that the morbid 

 condition originates in the introduction of a poison into the blood. The same 

 may be said of the Croup-like Convulsion or Crowing Inspiration of Infants, 

 which is an obstruction to the passage of air through the Glottis, produced 

 by a spasmodic contraction of the constrictors of the larynx; for, although 

 the spasmodic action may be immediately brought on by various kinds of 

 local irritation, such as that occasioned by teething, by the presence of undi- 

 gested food, or by intestinal disorder, yet there is no doubt that the excitable 

 condition of the Nervous Centres, without which these influences would be in- 

 operative, is dependent upon a defect of nutrition arising from unwholesome food, 

 bad air, or some other cause affecting the system generally. 1 Spasmodic closure 

 of the Larynx may occur from other causes. When the rima glottidis is nar- 

 rowed, by effusion of fluid into the substance of its walls, it is very liable to be 

 completely closed by spasmodic action, to which the unduly irritable condition 

 of the mucous membrane will furnish many sources of excitement. Choking, 

 again, does not result so much from the pressure of the food on the air-passages 

 themselves, as from the spasmodic action of the larynx excited by this ; and the 

 dislodgment of the morsel by an act of vomiting is the most effectual means 

 of obtaining relief. Tenesmus and Strangury are well-known forms of spas- 

 modic muscular contraction, excited by local irritation acting through the Spinal 

 centres. The abnormal action which leads to Abortion (CHAP, xix.) is fre- 

 quently excited in the same manner. There is a form of Incontinence of Urine, 

 which is very analogous to the morbid action just described; the sphincter has 

 its due power; but the stimulus to the evacuation of the bladder is excessive in 

 strength and degree, owing to the acridity of the urine or other causes. The 

 part of the bladder upon which this appears chiefly to act is the trigonum (which 

 is well known to be more sensitive to the irritation of calculi than the rest of 

 the internal surface) ; and Sir C. Bell advises young persons who suffer during 

 the night from this very disagreeable complaint, to lie upon the belly instead of 

 the back, so that the contact of the urine with the trigonum may be delayed as 

 long as possible. 



xvni. As convulsive diseases are dependent upon excessive activity of the 

 Spinal centres, so do various forms of Paralysis arise from disease of the Cord, 

 affecting its proper ganglionic substance, or the connections of its nerve-roots 

 with the Encephalon. If the latter only be impaired, we have an interruption of 

 sensibility and voluntary motion, the reflex actions of the Spinal ganglia being 



1 The influence of " change of air" is often as marked in this disease, as it is in the 

 chronic stage of hooping-cough. That an impure atmosphere is of itself sufficient to induce 

 fatal convulsive disorders in infants, has been sufficiently proved on a former occasion 

 (2 683). 



