968 



A MANUAL OF PHYSIOLOGY 



tastes of various kinds may be perceived. Sometimes this may be 

 due to the stimulation of substances excreted in the saliva ; but in 

 other cases it seems that, without passing beyond the blood and 

 lymph, foreign substances may excite the gustatory nerves. 



Flavour embraces a group of mixed sensations in which smell and 

 taste are both concerned, as is shown by the common observation 

 that a person suffering from a cold in the head, which blunts his sense 

 of smell, loses the proper flavour of his food, and that some nauseous 

 medicines do not taste so badly when the nostrils are held. 



In common speech, the two sensations are frequently confounded 

 with each other and with tactile sensations. Thus the ' bouquet ' 

 of wines, which most people imagine to be a sensation of taste, is in 

 reality a sensation of smell ; the astringent ' taste ' of tannic acid is 

 not a taste at all, but a tactile sensation ; the ' hot ' taste of mustard 

 is no more a true sensation of taste than the sensation produced by 

 the same substance when applied in the form of a mustard poultice to 

 the skin. 



Tactile and Common Sensations. 



Under the sense of touch it is usual to include a group of sensa- 

 tions which differ in quality and that in some instances to as 

 great an extent as any of the sensations 

 which are universally considered as separate 

 and distinct but agree in this, that the 

 end-organs by which they are perceived 

 are all situated in the skin, the mucous 

 membranes, or the subcutaneous tissue. 

 Such are the common tactile sensations 

 including pressure, tickling, and itching 

 and the sensations of temperature, or, 

 more correctly, of change of temperature, 

 or of warmth and cold. The sensation of 

 pain, although it cannot be absolutely 

 separated from these, ought not to be 

 grouped along with them. It is called 

 forth by the stimulation of afferent nerve- 

 fibres in their course ; and it may originate, 

 under certain conditions, in internal organs 

 which are devoid of tactile sensibility, and 

 secting black lines are the functional activity of which in their 

 normal state gives rise to no special sen- 

 sation at all. The peculiar sensation asso- 

 ciated with voluntary muscular effort, to 

 which the name of the muscular sense 

 has been given, also deserves a separate place ; for although it 

 may in part depend on tactile sensations set up through the 

 medium of end-organs situated in muscle, tendon, or the struc- 

 tures which enter into the formation of the joints, other elements 

 are, in all probability, involved. 



FIG. 426. TACTILE 

 CORPUSCLE FROM 

 SKIN OF FINGER 

 (SMIRNOW). 



the non-medullated 

 endings of the one or 

 more nerve-fibres that 

 enter the corpuscle. 



