1184* 



TOUCH. 



quences, the patient still being "quite con- 

 scious of the mere contact."* 



Reference has been already made to the 

 influence of the attention on the acuteness of 

 sensations; and to the slight degree in which 

 they are felt, when the mind is completely 

 engrossed in some other feeling or idea. This 

 is sometimes seen in spontaneous reverie ; 

 and there are individuals who can exert such 

 a power of mental abstraction, as voluntarily 

 to concentrate their attention on some ex- 

 ternal object, or internal idea, so as to escape 

 all suffering from a severe operation. This, 

 however, is much better seen in some of those 

 cases of somnambulism (see SLEEP) in which 

 the mind is completely under the guidance of 

 the suggestions received from without, its 

 whole spontaneous directing power being 

 suspended. For it is frequently possible, in 

 such cases, to withdraw the patient's atten- 

 tion from any part of the body, to such an 

 extent that the anaesthesia is complete as 

 regards that part, whilst every other portion 

 enjoys the ordinary sensibility. Thus a tem- 

 porary loss of sensation on the whole of one 

 side may be induced, or a single limb may be 

 rendered anaesthetic ; and the sensibility of 

 the parts may be instantaneously restored, 

 merely by directing the patient's attention 

 towards them. 



With regard to hyper<ssthesia, or increased 

 sensibility, we have much less definite in- 

 formation. There can be no doubt, however, 

 that it, too, may proceed from changes either 

 in the periphery, or in the central organs, and 

 perhaps also from an alteration in the trunks 

 of the nerves in their course. The acute 

 sensibility of an inflamed or irritated part is 

 an example of the first of these conditions ; 

 and the extraordinary exaltation of sensibility 

 in the incipient stage of phrenitis may serve 

 as an illustration of the second. In some cases 

 the entire nervous system would seem to 

 partake of this undue excitability ; this we 

 especially see in hysterical subjects, in whom 

 the slightest contact frequently occasions in- 

 tense suffering, so that even the mere pointing 

 of a finger at any part of the body will cause 

 a scream of alarm. The sufferings of such 

 persons are not rightly designated as ima- 

 ginary; they are as real to them as are those 

 proceeding from far more serious causes to 

 persons of less excitable temperament. The 

 fault partly lies in the habitual attention 

 which they pay to the most trivial feelings ; 

 but in part also, it may be surmised, to an 

 abnormal state of nutrition of the entire 

 nervous system, both centres and trunks, 

 from depravation of the blood. This view 

 harmonizes well with the fact just now stated, 

 that in the Epidemic de Paris, a temporary 

 hyperaesthesia (afterwards giving place to an- 

 aesthesia) was commonly among the earliest 

 symptoms. And it is not a little curious 

 that in the remarkable scries of cases of lead- 

 poisoning which recently occurred in the ex- 

 royal family of France, during their residence 



* Archives Generales, torn. xvi. pp. 5 24. 



at Claremont, the same symptom presented 

 itself, and was in some instances the only 

 symptom which indicated the morbid con- 

 tamination of the blood.* In most cases of 

 this form of hyperaesthesia, the exaltation 

 of sensibility seems confined to the surface, 

 being much more excited by a slight touch 

 than by hard pressure ; and this difference 

 will frequently serve to distinguish the " hys- 

 terical" tenderness from that of inflammation, 

 in which the pain is augmented the more 

 severe the pressure. The writer has had 

 opportunities of noticing an extreme sensi- 

 tiveness to changes of temperature in certain 

 cases of somnambulism, both natural and 

 artificial ; and he believes that this fact affords 

 a ready solution of various marvels which 

 have been narrated touching the power of 

 " mesmerized" subjects to distinguish a piece 

 of money which had been held in the mes- 

 merizer's hands, or a glass of water in which 

 his finger had been immersed. 



It has recently been proposed to apply 

 Prof. Weber's method of estimating the re- 

 lative acuteness of the tactile sense in dif- 

 ferent parts of the body, to the determination 

 of the degree of anaesthesia or of hyper- 

 aesthesia, in patients affected with these dis- 

 orders. Thus it was found by M. Brown- 

 Sequard that in one case of nearly complete 

 anaesthesia of the lower extremities, the pa- 

 tient only felt a single impression on the 

 skin of his legs, when the points of the com- 

 passes were from 10 to 20 centim. apart ; the 

 normal "limit of confusion" for this portion 

 of the surface being from 3 to 5 centim. In 

 another case of slighter anaesthesia, the " limit 

 of confusion" in the same part was from 9 

 to 15 centim. And in a third case of very 

 slight anaesthesia, it was from 6 to 7 centim. 

 In a case of hyperaesthesia, on the other 

 hand, which accompanied paralysis of the 

 motor power, the patient could perceive the 

 distinctness of the two points on the foot, 

 when they were separated to the distance 

 of only 5 millim., although the normal " limit 

 of confusion " in that part was from 25 to 30 

 millim. The sensibility to pain, in this case, 

 was as much exaggerated as was the tactile 

 sensibility. 



Of the depravation of tactile sensibility, 

 manifested in a variety of morbid phenomena, 

 such as the sense of heat or even of burning 

 (without any real elevation of temperature), 

 of formication, of tickling, of itching, &c., 

 it must suffice here to remark, that this, like 

 the preceding affections, may be due to causes 

 acting on the peripheral nerves, or on the 

 nervous centres, or on the connecting trunks. 

 Of the latter we have a good example in the 

 formication which generally succeeds complete 

 anaesthesia, when a nerve has been pressed 

 upon for a time, and the pressure is then re- 

 moved. 



W. JB. Carpenter. 



* See Dr. Gueneau de Mussy's Cases of Poisoning 

 by Lead at Claremont, in Dublin Quarterly Medical 

 Journal, May, 1849. 



