170 PHYSIOLOGY CHAP. 



man, at any rate by other animals, when they reach the olfactory 

 area of the nasal mucous membrane along with the inspired air. 



Tourtual (1827) stated that odours are only perceptible -in the 

 gaseous state. E. H. Weber (1847) gave support to this view by 

 a number of experiments. He bent his head so far back that the 

 nostrils were directed upwards, and then injected water into the 

 nasal fossae so that the olfactory region should be as full as 

 possible. He found that when the water had run out, the function 

 of smell was lost for 30 seconds, and then returned gradually, but 

 did not become normal again for 2 J minutes. A solution of sugar 

 had the same effect as pure water. The injection of water scented 

 with eau de cologne produced a smell at the first moment of 

 injection ; but all olfactory sensation disappeared when the nasal 

 cavity became full ; on emptying it smell was abolished for a time, 

 as on injecting pure water. Valentin (1848) confirmed Weber's 

 results, and found that on emptying the nose of the injected water 

 the tactile nerves of the nasal mucosa recover their activity 

 before the olfactory nerves. Frohlich (1851) obtained much the 

 same results. 



The loss of olfactory sensibility thus produced depends, 

 according to Weber, on the saturation of the olfactory epithelial 

 cells of Schneider's membrane with water, which checks their 

 function. But it is more correct to suppose that the injection of 

 plain water, particularly at a low temperature, alters the epithelium 

 of the nasal mucous membrane, and causes a nasal catarrh which 

 is sufficient of itself to produce diminution or total inhibition of 

 olfactory activity. 



According to Aronsohn (1886), Weber's theory that odours are 

 imperceptible in a watery solution is erroneous. On Kronecker's 

 suggestion he substituted a solution of physiological saline for the 

 pure water douche, adding an odoriferous substance and raising the 

 temperature to 38 C. He used 0-5 c.c. oil of cloves in 250 parts of 

 saline at 38, and was able to smell it, on filling the nasal cavities 

 by a nasal douche apparatus, for 30-40 seconds. Temperatures 

 above the normal (38-44 C.) are more favourable than lower 

 temperatures, perhaps because they increase the excitability of the 

 olfactory nerves. 



Aronsohn also experimented with camphor, eau de cologne, 

 cumarine, and vanilla. The degree of dilution of these odours 

 required to evoke a definite sensation, and also the concentration 

 required for solutions to reach the threshold of excitation, vary. 

 The indifferent (isotonic) solution of sodium chloride is 0-7-0-75 

 per cent, preferably 0-73 per cent, which corresponds with the 

 fact discovered by Kumsberg that the tissue fluids contain 0-62- 

 0.73 per cent sodium chloride. 



Sodium chloride may be replaced by other salts, each of which 

 has an optimum degree of concentration which is indifferent to 



