ODORS AND LIFE. 181 



ing something, and is resorted to for the sake of a keener 

 sensation, we first close the mouth, and then sometimes 

 draw in a full breath, sometimes a succession of short, 

 quick inspirations. Then the muscular apparatus edging 

 the opening of the nostrils comes into play, to contract 

 that orifice, and point it downward, so as to increase the 

 intensity of the current of inhaled air. When, on the con- 

 trary, we wish to smell as little as possible, the organ be- 

 comes passive. "We effect strong expirations by the nose 

 to drive out the air that produces scent, and inhalation, 

 instead of being performed by the nostrils, instinctively 

 takes place through the mouth. 



Scents and the sense of smell have an important share 

 in the phenomena of gustation, that is, there is a close con- 

 nection between the perception of odors and that of tastes. 

 Physiological analysis has clearly brought out the fact that 

 most of the tastes we perceive proceed from the combina- 

 tion of olfactory sensations with a small number of gusta- 

 tory sensations. In reality, there are but four primitive 

 and radical tastes sweet, sour, salt, and bitter. A very 

 simple experiment will convince us of this fact. If we 

 keep the nostrils closed when tasting a certain number of 

 sapid substances, so as to neutralize the sense of smell, the 

 taste perceived is invariably reduced to one of the four 

 simple savors we have just named. Then, whenever the 

 pituitary membrane is out of order, the taste of food is no 

 longer the same ; the tongue distinguishes nothing but 

 sweet, sour, salt, or bitter. 



It is time now to begin the study of the physiological 

 and chemical conditions of smell, and for this we must first 

 inquire how odorous substances behave with regard to the 

 medium which separates them from our organs. PreVost, 

 in an essay published in 1799 on the means of making 

 emanations from odorous bodies perceptible to sight, was 

 the first to bring to view the fact that certain odorous sub- 



