476 Dynamic Theory. 



Others smell bad many hydrogen compounds, &c. : Sulphuretted 

 hydrogen, phosphoretted hydrogen, arseniuretted hydrogen, bisulphide 

 of carbon, and other volatile hydrocarbons ; also many compound or- 

 ganic bodies, especially those formed by organic decomposition. In 

 general, bad smelling things are repugnant to health, although all nox- 

 ious substances do not give this warning. The gases which have a great 

 tender :/ to combine and to react rapidl} r upon organic tissues are odor- 

 ous. Sulphuretted hydrogen decomposes the blood, turning it black, and 

 chlorine, iodine, bromine and ammonia rapidly destroy organic substances. 

 The vapors, alcohol, ether and chloroform, all rapidly act on organic 

 tissues. The gases which are not odorous act slowly or not at all chem- 

 ically on organic tissues, as hydrogen, carbonic acid, oxygen, except 

 when oxygen is in its active state, ozone, and then it lias an odor. A 

 great many smells of food, &c. , are very agreeable when we are hungry 

 and not when we are full. ( Bernstein. ) 



This sense, like all the others, is subject to hallucinations and illusions 

 which arise from the fact that the nerves can be stimulated by other 

 agitations than those coming through the sense organ. The organ itself 

 can be impressed only by the forces which have differentiated it, or by 

 some forces closely akin to them. But the conveying nerve fibre ( as 

 well as the corresponding brain cell ) receives every stimulus as if it 

 came from its own proper sense organ. If, therefore, an olfactory nerve 

 fibre, differentiated to convey the smell of wine for example, should be 

 touched or stimulated at a point between the pituitary membrane and 

 the brain, the stimulus would pass into the brain as a veritable odor of 

 wine, and unless some other sense should expose the deceit, the illusion 

 that wine had actually been smelled would be complete. Disease or in- 

 juries of the olfactory bulb or of the anterior lobe of the brain have 

 been known to produce delusion of smell. A case is recorded in which 

 a man after a fall from a horse always fancied that he smelled a bad 

 odor. (Neil & Smith.) Sometimes temporary delusion may arise from 

 a revived memory of an odor. The brain cells devoted to the perception 

 of that odor become erected abnormally and produce the false percep- 

 tion. A certain woman smelt the odor of musk whenever she saw a 

 well dressed woman passing ; and smelt tobacco when a man went by. 

 Another could not bear the smell of the rose and became sick upon see- 

 ing an artificial one, the false sense of the odor being arroused by the 

 imagination. ( Papillon. ) 



The mode of action of the sense as generally explained is simple 

 enough. Odorous substances are those that cast off into the air infi- 

 nitely minute particles of their substance. These particles passing into 

 i.he nasal channels with the inhaled oxygen of the air come into contact 

 with the pituitary membrane and stimulate or excite it. This stimula- 



