382 FUNCTIONS OF THE NERVOUS SYSTEM. 



limited to the Brain, we may infer that one of these systems is involved. Dr. 

 M. Hall has recently pointed out, that this complication is due to the impres- 

 sions made upon the fibres of the Spinal nerves distributed upon the Dura 

 Mater, and other serous and fibro^ membranes ; for convulsive actions may 

 be induced by pinching these membranes, or otherwise irritating them. Of 

 the distinct forms or combinations, of which the class of convulsive disorders 

 is composed, Tetanus is one of the most interesting and instructive. This 

 disease is evidently dependent upon a state of undue excitability of the whofe 

 Spinal System ; and this may be produced by different causes. That which 

 is termed the idiopathic form of the disease has its origin in the centres ; it 

 may result in Man from the operation of various predisposing and exciting 

 causes: and may be artificially induced in Animals by the administration of 

 Strychnia. In the traumatic form of the disease, the morbid state has its 

 origin in a local injury; and the irritation propagated from this, and operating 

 through the Spinal Cord, may be itself a cause of many of the convulsive 

 movements. But, when the irritable state is once established in the nervous 

 centres, convulsive action of the muscles may be excited by any stimuli, and 

 even almost entirely without external causes. Hence it is that, whilst the 

 amputation of the injured part is not unfrequently the means of saving the 

 patient, if performed sufficiently early, it is attended with no benefit if delayed. 

 The Cerebral apparatus is entirely unaffected in this disorder; but the nerves 

 of deglutition are usually those first influenced by it; those of respiration, 

 however, being soon affected, as also those of the trunk in general. The 

 condition termed Hydrophobia is nearly allied to that of traumatic Tetanus, 

 differing chiefly in the mode in which the cranio-spinal axis is affected. The 

 irritable state of the nervous centres results from a local injury of a peculiar 

 kind; and here, too, the early removal of the part is very desirable as a means 

 of prevention ; although, when the malady has once reached the centres, it is 

 of no use. The muscles of respiration and deglutition are, as in Tetanus, 

 those spasmodically affected in the first instance ; but there is this curious 

 difference in the mode in which they are excited to action, that, whilst in 

 Tetanus the stimulus operates through the true Spinal Cord (either centrally, or 

 by being conveyed from the periphery), in Hydrophobia it is often conducted 

 from the ganglia of Special Sense, or even from the Cerebrum ; so that the 

 sight or sound of fluids, or even the idea of them, occasions equally with their 

 contact, or with that of a current of air the most distressing convulsions. It 

 would seem, therefore, as if the Serisori-motor system of nerves was involved 

 in it.* In these and other general convulsive diseases, it is probable that the 

 whole vesicular matter of the centres involved is in so excitable a state, that 

 a stimulus applied to any part of it may produce a reaction through the whole. 

 In no other way would it be easy to explain the great number and variety of 

 movements, which a small degree of local irritation may excite. 



503. Epilepsy is another convulsive disease, principally involving the Spinal 

 Cord, but partly affecting the Brain. The predisposition to convulsive move- 

 ments may depend upon many causes ; but the movements themselves are in 

 general immediately excited by some local irritation, as by the presence of 

 undigested matter in the stomach, of worms in the intestines, &c., although 

 frequently also from causes purely mental. The convulsive movements usually 

 affect the muscular system very extensively ; acting especially upon the mus- 

 cles of ingestion and egestion. The Brain is evidently much concerned in 

 the disease, however; as is evident from the numerous instances in which it 

 has been clearly traced to some local affection of that organ, as well as from 



* For an interesting case of the excitement of involuntary muscular movements, by sen- 

 sations received through the eye and ear, see Dr. Cowan, in Lancet for 1840. Vol. II., p. 364. 



