836 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



cated, this disease must be regarded as consisting essentially in a diminution of 

 the power of the Will (exerted through the Cerebrum) over the muscular ap- 

 paratus, concurrently with an augmented and perverted activity of the Sensori- 

 motor centres. That its special seat is at the summit of the Cranio-Spinal axis, 

 where it comes into connection with the Cerebrum, would appear from several 

 considerations, particularly from the interruption of voluntary power, the aggra- 

 vation of the movements by emotion, and their cessation during sleep ; the two 

 latter facts being inconsistent with the idea that the proper Spinal centres are 

 essentially involved,- although they are frequently affected coincidently or sub- 

 sequently. The choreic convulsion is occasionally hemiplegic ; and it sometimes 

 gives place to paralysis, which is seldom complete, however, and may usually be 

 cured by appropriate treatment. This disorder appears generally traceable to a 

 state of imperfect nutrition, dependent upon a depraved and perhaps a poisoned 

 state of the blood, rather than on any organic lesion. 1 Not unfrequently the 

 defect of nutrition seems to act as the " predisposing cause" of the disease; the 

 attack being immediately traceable to mental emotion. 2 Stammering may be 

 regarded as a sort of Chorea, affecting the muscles of Voice. 



x. The Sensory Ganglia, collectively constituting the Sensorium, may be 

 regarded as the most essential part of the Encephalon; since we find them fully 

 developed in animals which scarcely possess a rudiment of a Cerebrum, and 

 presenting the same relative condition to the latter in the early embryo of Man. 

 They directly receive the nerves proceeding from the organs of Special Sense, 

 each pair of which has its own distinct ganglionic centre; and they receive, also, 

 through the (so-called) Crura Cerebri, the nerves of " common sensation/' whose 

 ganglionic centre appears to lie in the Thalami Optici. They give off a large 

 number of motor fibres, which, descending through the Crura Cerebri, are distri- 

 buted, with the fibres proceeding from the Spinal ganglia, through the various 

 motor trunks, to the muscular system generally. 3 On the other hand, by one 

 set of the radiating fibres of the Cerebral substance, they transmit sensorial im- 

 pressions upwards to the vesicular surface of the Hemispheres; whilst conversely, 

 by its descending fibres, they receive the impressions transmitted downwards 

 from the Cerebral ganglia ; and they thus constitute the medium by which alone 

 the Cerebrum communicates with the Organs of Sense on the one hand, and 

 with the muscular apparatus on the other. The Sensory Ganglia must be 

 collectively regarded as forming the organ through whose instrumentality the 

 Mind is rendered conscious of impressions made on the Organs of Sense ; and 

 reasons have been advanced for the belief, that it also serves as the instrument 

 whereby the Consciousness is affected by Cerebral changes, which, in so far as 

 they take place independently of the Will, are the cause and not the consequence 

 of Mental activity. There is no reason to think that the Sensorium has in itself 

 any higher function than that of impressing the consciousness of the individual; 

 this impression on the consciousness, when made by an external agency operat- 

 ing through the sensory nerves, is that which is known as Sensation; but, 

 when produced by Cerebral changes, it constitutes Ideation. With the states 



1 See Dr. Todd's Lumleian Lectures "On the Pathology and Treatment of Convulsive 

 Diseases" in the " Medical Gazette," April 20 and 27, 1849. 



2 A remarkable number of cases of Chorea were admitted into the Bristol Infirmary 

 within a few weeks after the memorable Riots of 1833. 



3 The doctrine previously advocated (g 701), that there is an actual continuity of fibres 

 between the Sensorial centres and the roots of the Spinal Nerves, has lately received very 

 important confirmation from the elaborate researches of Dr. Turck on the alterations pro- 

 duced in the Spinal Cord by Hemiplegia originating in intra-cranial lesion. See his 

 Memoir " Uber secondiire Erkrankung einzelner lliickensinarksstriinge und ihrer Fortset- 

 zungen zum Gehirne,"in " Denkschriften der kaiserlichen Academic der Wissenschaften," 

 Wein, 1851. 



