PHYSIOLOGY. 



cpmmodate that organ to a greater or less 

 number of rays, according to the effect 

 they produce. 



An entire state of the membrana tym- 

 pani is not essential to hearing; for the 

 sense remains, where an opening has 

 taken place in that part , yet it is neces- 

 sary that the tympanum should communi- 

 cate with the fauces, for an obstruction 

 of the eustachian tube causes deafness. 



Vibrations may be transmitted to the 

 auditory nerves through -the bones of the 

 head; thus a watch placed between the 

 teeth is heard very distinctly, although 

 the ears are stopped, &c. 



Smelling. The odorous effluvia of bo- 

 dies are disseminated in the atmosphere. 

 The latter fluid passes through the nose 

 in respiration, and thereby brings the 

 odorous particles into contact with the 

 olfactory nerves, which convey the im- 

 pressions of odours to the brain. It is in 

 the first pair of nerves only that the sense 

 of smelling is supposed to reside, while 

 the numerous twigs of the fifth pair that 

 are distributed in the nose, are merely 

 for the purpose of general sensibility. 

 Hence we see two very distinct modes of 

 sensibility in this part, one of which may 

 be entirely obliterated, while the other is 

 augmented; in violent coryza the ordi- 

 nary feeling is very acute, for the pitui- 

 tary membrane is painful; but the per- 

 son at the same time is not conscious of 

 the strongest odours. 



As air is the vehicle of odours, its pas- 

 sage through the nose, in ordinary respi- 

 ration, is sufficient for the purpose of 

 smelling ; but when any odour is particu- 

 larly agreeable, we make short and re- 

 peated inspirations, and at the same time 

 shut the mouth, that the air, which enters 

 the lungs, may pass entirely through the 

 nose. On the contrary, we breathe by the 

 mouth, or entirely suppress respiration, 

 when odours are unpleasant to us. 



The small distance between the origin 

 of the olfactory nerves in the brain, and 

 their termination in the nose renders the 

 transmission of impressions very sudden 

 and easy. This induces us to apply to the 

 nose stimuli that are proper to revive 

 sensibility when life is suspended, as in 

 cases of fainting, suffocation, &c. 



Tasting. No body can affect the organ 

 of taste, that is not soluble at the ordi- 

 nary temperature of the saliva. Hence the 

 chemical maxim, " corpora non agunt 

 nisi soluta," may be very justly applied to 

 this sense. If the tongue be completely 

 dry, and a body applied to it be also dry, 

 no sense of taste ensues, as any one may 



convince himself by wiping his tongue 

 dry, and applying sugar to it. The state 

 of the tongue's surface, which is well 

 known to depend much on the condition 

 of the stomach, also impairs our sense of 

 taste ; hence in some disorders every 

 thing tastes bitter. 



No sense approaches more nearly to 

 feeling than this does; and the organ 

 bears a considerable analogy to that of 

 the sense of touch. The superior papil- 

 lous surface of the tongue is the organ of 

 taste, but we cannot deny the power of 

 discerning savours to other parts of the 

 mouth ; bitter substances are particularly 

 tasted about the throat; and in some in- 

 stances, where large portions, or the 

 whole tongue, have been cut away or 

 destroyed, a perception of tastes has still 

 remained. The lingual branch of the 

 fifth pair is considered as the true gusta- 

 tory nerve, while those sent to the tongue 

 by the eighth and ninth are regarded as 

 merely nerves of motion. Although the 

 tongue appears to be a single organ, it 

 consists of two symmetrical halves ; and 

 should be considered as a distinct right; 

 and left organ closely applied to each 

 other. This is shewn in hemiplegia, 

 where one-half only is paralysed. 



Touching. The whole surface of the 

 skin is the organ of this sense, which 

 gives us information concerning more 

 properties of extraneous bodies than any 

 other of our senses. The sight, hearing, 

 smell, and taste, are confined to circum- 

 scribed limits; while the touch, distributed 

 on the whole surface, effectually pro- 

 vides for our preservation, by giving us 

 notice of the approach of external bodies, 

 and informing us of their properties. 

 Every thing that is not sound, light, 

 odour, or savour, is appreciated by this 

 sense, as the temperature, consistence, 

 dryness, or moisture, magnitude, dis- 

 tance, &c. of objects. It corrects the er- 

 rors of sight and the other senses, of 

 which it may indeed be justly termed the 

 regulator; and, above all others, furnishes 

 us with the most certain and exact ideas. 

 Exercise and cultivation bring it to a 

 wonderful degree of perfection, so that 

 in blind persons it may almost be said to 

 supply the loss of sight ; in some such in- 

 stances different colours and their various 

 shades have been distinguished by its 

 assistance. 



Although the tangible qualities of bo- 

 dies can be perceived by every part of 

 the cutaneous organ, it possesses in some 

 situations a more delicate structure, con- 

 sisting 1 of fine pointed prominences, called 





