386 SPECIAL PHYSIOLOGY. 



turpentine or ether, do positively waste, so that the inference, at pres- 

 ent, is in favor of the actual transmission of material particles through 

 the air, until they are brought into contact with the nasal mucous 

 membrane. The interposition of a solid body between an odorous 

 substance and the nose, prevents th^ transmission of the odor, which, 

 therefore, cannot be conducted, like sound, by vibrations, nor, like 

 light, by undulations. Odorous emanations are capable of being ab- 

 sorbed by porous substances or materials, such as cloth, especially, it 

 is said, by dark cloths, which are therefore unsuited for medical men 

 and nurses in fever hospitals. When absorbed by fresh animal char- 

 coal, odors are, like the compound gases, partially subjected to decom- 

 position by a process of slow oxidation. 



Smell. 



Every portion of the nasal mucous membrane possesses common 

 sensibility and its modifications, being alike capable of receiving im- 

 pressions of touch, temperature, and pain. This is owing to the pres- 

 ence of the branches of the fifth pair of nerves. It is probable even, 

 as already hinted, in speaking of carbonic acid, that many strong 

 vapors, such as ammonia, acetic, and other volatile acids, not merely 

 affect the true nerve of smell, but also the branches of the fifth nerve, 

 causing that combination of odor and irritation, which characterizes 

 the so-called pricking or pungent odors. These substances appear 

 indeed, to act, when highly diluted, as odors, but when less diluted, or 

 concentrated, as irritants, just as they act on the cutis, and excite a 

 pricking or smarting sensation when the cuticle is removed. 



The sense of smell proper, however, is shown, by the following facts, 

 to be dependent on the action of the olfactory nerves, and of the spe- 

 cial olfactory lobes or centres. First, the size of these nerves and 

 lobes, in animals distinguished for their perfect sense of smell ; sec- 

 ondly, the abundant distribution of the nerves in the upper part of the 

 nose ; thirdly, the absence of the sense of smell in congenital. deficiency 

 of the olfactory lobes and nerves, of which an instance occurred in a 

 street scavenger at Leipsic ; fourthly, the loss of the sense of smell in 

 diseases affecting the olfactory lobes, and the upper or olfactory region 

 of the nose ; and lastly, the similar loss of smell, following the division 

 or destruction, of these lobes in animals. This experiment is most 

 easily performed in young animals. (Biffi.) 



It was found by Ma gen die, that dogs in which the olfactory nerves 

 had been destroyed, still searched for, and discovered, meat. This fact, 

 he thought, justified the extreme conclusion that the olfactory nerves 

 were not in any way concerned in smell;, but it is rather to be ex- 

 plained, by reference to the instinct and habits of the dog, which would 

 lead it to search for food, even though it could not smell. Paralysis 

 of the fifth cranial nerve, diminishes the healthy secretion of the nasal 

 mucous membrane, and so interferes with the sense of smell. 



The conditions necessary to smelling are these. First, the trans- 

 portation through the air of the odorous particles, in the manner al- 

 ready mentioned, to the nose ; this is more rapid when the air is in 



