1172 



TOUCH. 



contact with the denuded surface ; so that one 

 of these patients thrice affirmed that he was 

 being touched with the cold body when it 

 was the warm, and the reverse. But when 

 the spatula was in one instance made some- 

 what warmer, and was brought into contact 

 with the uuskinned surface, the patient felt, 

 not heat but pain. Another means of gaining 

 information on this point is afforded by the 

 ingestion or injection of a large quantity of 

 warm or cold fluid into the stomach or intes- 

 tinal canal. Thus Professor Weber states, 

 that after drinking a tumbler of water at 32, 

 he felt the cold water in the mouth, in the 

 palate, and in the pharynx, as far as the limits 

 of the sense of touch ; but that the gradual 

 passage of the cold water into the stomach 

 could not be perceived. There was, it is 

 true, a slight sensation of cold in the gastric 

 region ; but as it only occupied the situation 

 of the anterior wall of the stomach, it was at- 

 tributable to the abstraction of heat from the 

 abdominal integuments in contact with this. 

 In an opposite experiment, the author drank 

 quickly three glasses of milk, the temperature 

 of the first of which was 158, that of the 

 second 14<5, whilst that of the third was in- 

 termediate between the two. The sensation of 

 heat could not be traced lower down than 

 that of the cold in the previous experiment. 

 At the moment when the fluid entered the 

 stomach, there was a feeling which remained 

 for some time, but which could not be dis- 

 tinguished as heat, being mistakeable for cold. 

 In order to ascertain the sensations produced 

 in the large intestine by cold water, an in- 

 jection of 1-iozs. of water of the temperature 

 of 65 was thrown up the rectum, but scarcely 

 any sensation of cold could be perceived from 

 it. In another instance, 21 ozs. of water at 

 the same temperature was thrown up, without 

 any resulting sensation of cold. In both these 

 cases, on the return of the enema a few mi- 

 nutes afterwards, a distinct feeling of cold was 

 experienced at the anus. When water of so 

 low a temperature as 45J was injected, the 

 first feeling excited was a sensation of cold in 

 the immediate neighbourhood of the anus, and 

 then a feeble movement in the bowels ; but a 

 little time afterwards, there was a faint sensa- 

 tion of cold, especially in the anterior wall of 

 the abdomen. This sensation, however, re- 

 mained after the return of the water ; and 

 may hence be attributed to the abstraction 

 of warmth from the abdominal integuments, 

 which was proved to take place, the temper- 

 ature of the surface being lowered .3 degrees. 

 So, again, if the cavity of the nose be filled 

 with cold water, the coldness is only perceived 

 in the parts of the cavity which are most en- 

 dowed with the proper tactile sense, namely, 

 the neighbourhood of the nostrils and of the 

 pharynx ; and it is not at all discernible in 

 the higher part of the cavity, which is espe- 

 cially subservient to the olfactive sense. [See 

 SMELL.] But when the water injected is very 

 cold (e. g. 41), a peculiar pain is felt in the 

 upper part of the nasal fossae, extending to 

 the regions of the forehead and lachrymal 



canals ; this pain, however, is altogether dif- 

 ferent from the sense of coldness. 



From the foregoing experiments it appears 

 fair to conclude, that the sensory nerves have 

 no power of receiving impressions arising from 

 difference of temperature, unless those im- 

 pressions are communicated through a special 

 organ ; but they afford no adequate ground for 

 the supposition, that a set of nerve-fibres is 

 provided for their transmission, distinct from 

 those which minister to common sensation. 

 This conclusion is confirmed by the fact, that 

 we cannot excite impressions of heat or cold 

 by direct application to the trunks of nerves 

 which we know must conduct such impres- 

 sions. Thus the parts of the skin immediately 

 beneath which lie large nerve-trunks, are not 

 more sensitive to moderate heat or cold than 

 any other part ; whilst a greater degree of 

 either is felt as pain, not as a change of tem- 

 perature. Tims, as we have already seen, a 

 mixture of ice and water, applied over the 

 ulnar nerve, affects it in fifteen seconds, and 

 produces severe pain, having no resemblance 

 to cold, such as cannot be excited by the 

 same cold applied to any other region. So 

 the nerve of the tooth-pulp is equally and 

 similarly affected by water of 43 and of 112; 

 either application causing a pain exactly 

 similar to that excited by the other, or that 

 produced by pressure.* 



We have now to consider those more com- 

 plex modes of exercise of the sense of touch 

 which require the conjoint exercise of the 

 " muscular sense;" and as this is a modifi- 

 cation of the general sensibilitv, which may 

 perhaps be regarded as being as special or 

 peculiar in its relations to the muscular sys- 

 tem as the sense of touch (properly so called) 

 is to that of the skin,jit will be desirable to 

 examine, in the first instance, into its modus 

 operandi. 



Muscular Sense. It may be stated as a 

 general fact, that all voluntary muscular con- 

 traction must be guided and controlled by sen- 

 sation ; and in the majority of cases, the con- 

 trolling sensation is derived from the muscles 

 themselves, of whose condition we are ren- 

 dered cognisant by the sensory nerves with 

 which they are furnished. The proof of this 

 necessity is furnished by the entire want of 

 power to make or sustain voluntary efforts, 

 when the guiding sensation is deficient. Thus, 

 in complete anassthcsia of the lower extre- 

 mities, without loss of muscular power, the 

 patient is as completely unable to walk, as if 

 the motor nerves had also been paralysed, 

 unless the deficient sensorial guidance be re- 

 placed by some other ; and in similar affections 

 of the upper extremities, there is a like in- 

 ability to raise the limb or to sustain a weight. 

 But in such cases, the deficiency of the " mus- 



* It is remarkable that the same should be true 

 of the impressions received through the skin itself, 

 when they pass beyond certain limits of intensity ; 

 thus, the sensation produced by touching frozen 

 mercury is said to be not distinguishable from that 

 which results from touching a red-hot iron. 



