OLFACTORY SENSATIONS. 823 



bones covered by the olfactory mucous membrane. 2. The cencentration of the 

 odorous mixture of the air. Still, some substances may be attenuated enormously 

 (e.g., musk to the two-millionth of a milligramme), and still be smelt. 3. The 

 frequency of the conduction of the vapour to the olfactory cells (sniffing). 



[The acuteness of the sense of smell is greatly improved by practice. A boy 

 named James Mitchell, who was deaf, dumb, and blind, used his sense of smell, 

 like a dog, to distinguish persons and things.] 



[As in the case of sight and hearing, it has been sought to connect the quality of taste and 

 smell with the kind of vibrating stimulus. Ramsay showed that many facts pointed to the 

 dependence of smell upon the vibratory motion of odorous particles ; thus, many gases and 

 vapours of low specific gravity i.e., with a very rapid vibration of their molecules are per- 

 fectly odourless, while such substances as the alcohols and fatty acids, alike in chemical and 

 physical properties, can excite generic smells, the higher members of the group being more 

 powerful in this respect than the lower ones. Taking the elements as arranged in a "Natural 

 Classification" by Mendelejeff, Haycraft has shown that elements in the same group are capable 

 of producing similar or related tastes, and the same seems to be true for smell {Haycraft).] 



We can smell the following substances in the following proportions : Bromine ^w^, sul- 

 phuretted hydrogen -gTnnnnr milligramme in 1 c.cm. of air (Valentin) ; also TBTmjin) ot a milli- 

 gramme of chlorphenol, and ^w^ -snnr of a milligramme of mercaptan (E. Fischer and Penzoldt). 



Electrical stimuli give rise to olfactory sensations. [Althaus found that electrical stimula- 

 tion of the olfactory mucous membrane gave rise to the sensation of the smell of phosphorus, 

 and Aronsohn found that he smelt on making the current when the cathode and on breaking 

 the current when the anode was in the nose. 



The variations are referred to in 343. If the two nostrils are filled with different odorous 

 substances there is no mixture of the odours, but we smell sometimes the one and sometimes 

 the other ( Valentin). [Some substances appear to affect some regions of the olfactory mem- 

 brane, while others affect other parts.] The sense of smell, however, is very soon blunted, or 

 even paralysed. [It can be blunted or fatigued in a few minutes ; but after it is completely 

 fatigued it can recover in. a minute.] Morphia, when mixed with a little sugar and taken as 

 snutf, paralyses the olfactory apparatus, while strychnin makes it more sensitive (Lichtenfels 

 and Frbhlich). 



The sensory nerves of the nasal mucous membrane ( 347, II.) [i.e., those supplied from the 

 fifth cranial nerve] are stimulated by irritating vapours, and may even cause pain, e,g., ammonia 

 and acetic acid. In a very diluted condition they may even act on the olfactory nerves. The 

 nose is useful as a sentinel for guarding against the introduction of disagreeable odours and 

 foods. The sense of smell is aided by the sense of taste, and conversely. 



[Flavour depends on the sense of smell, and, to test it, use substances, solid or fluid, with an 

 aroma or bouquet, such as wine or roast beef.] 



[Method of Testing. In doing so, avoid the use of pungent substances like ammonia, which 

 excite the fifth nerve. Use some of the essential volatile oils, such as cloves, bergamot, and the 

 foetid gum resins, or musk and camphor. Electrical stimuli are not available. Action of 

 Drugs, 343.] 



Comparative. In the lowest vertebrata, pits, or depressions provided with an olfactory 

 nerve, represent the simplest olfactory organ. Amphioxus and the cyclostomata have only one 

 olfactory pit ; all other vertebrates have two. In some animals (frog) the nose communicates 

 with the mouth by ducts. The olfactory nerve is absent in the whale. 



Historical. Rufus Ephesius (97 a.d.) described the passage of the olfactory nerve through 

 the ethmoid bone. Rudius (1600) dissected the body of a man with congenital . anosmia, in 

 whom the olfactory nerves were absent. Majendie originally supposed that the nasal branch of 

 the fifth was the nerve of smell, a view successfully combated by Eschricht. 



The Sense of Taste. 



422. STRUCTURE OF THE GUSTATORY ORGANS. Gustatory Region. 



There is considerable difference of opinion as to what regions of the mouth are 

 endowed with taste : (1) The root of the tongue in the neighbourhood of the 

 circumvallate papillae, the area of distribution of the glosso-pharyngeal nerve, is un- 

 doubtedly endowed with taste ( 351). (2) The tip and margins of the tongue are 

 gustatory, but there are very considerable variations. (3) The lateral part of the soft 

 palate and the glosso-palatine arch are endowed with taste from the glosso-pharyn- 



