10 PRACTICAL PHYSIOLOGY 



SMELL 



A bottle of vanilla is opened for a short time in the laboratory 

 where the students are at work, but not to a sufficient extent to 

 enable those at work to detect the smell. They then leave the 

 room and return. Is the odour now perceived ? What conclusion 

 may be drawn as to the way in which the sense of smell is stimulated. 

 Is it the amount of vanilla in the air or the change in the amount 

 of vanilla passing through the nose which stimulates ? 



The Difficulty of Classification and the Confusion of Taste with Smell. 

 The student closes his eyes, pinches his nose and opens his mouth ; 

 his companion places on the tongue pieces of apple. These are 

 replaced in turn by pieces of onion and pieces of potato. The sub- 

 stances may be rolled over the tongue, but should not be chewed, 

 because the texture is different in the three cases. The identification 

 is noted in the several cases and control experiments should be 

 made with the nose open. 



Compare the results of this experiment with the so-called loss or 

 impairment of taste during a " cold in the head." 



HEARING 



(Revise your knowledge of the physics of sound vibrations and 

 of the anatomy of the ear.) 



1. Examine the models of the middle ear, and study the way in 

 which an inward movement of the tympanum is transmitted by 

 the ossicles to the fenestra ovalis. Note especially the joint between 

 the malleus and incus and the way in which it is locked as the 

 tympanum is moved inwards and unlocked as the membrane is 

 moved outwards. 



2. Examine a section of the cochlea under a low power and 

 identify the scala vestibuli, scala tympani, scala media, basilar 

 membrane and organ of Corti. 



3. Examine a transverse section of the lower part of the 

 Eustachian tube. 



4. Close the mouth firmly and hold the nose so as to close the 

 nostrils. Then make a forcible expiration. Note the sensation 

 produced as air is driven up the Eustachian tube. 



5. One student closes his mouth. His companion then inserts the 

 nozzle of the Politzer's bag, covered with a small piece of rubber 

 tubing out of a 1 per cent, lysol solution, into one of his nostrils and 

 holds it in position with his finger and thumb, closing in this way the 

 other nostril. He then presses the bag gently and the subject 

 observes if he has a sensation of air entering the drum of the ear. 



The subject holds some water in his mouth, and as he swallows it, 

 his companion again compresses the bag with the same force as 

 before, and the subject observes whether air passes into the ear. 



What conclusion may be drawn as to the condition of the 

 Eustachian tube during swallowing ? 



