372 PRACTICAL PHYSIOLOGY. [LXXVI 



making a sound in front, the observed person will refer it to a 

 position beliind him. 



(/'.) Test the highest audible sound by means of Galton's 

 whistle. 



12. Dissection of the Middle Ear. — It is most important for the 

 student to do this. Use the head of a sheep. Remove the lower 

 jaw, expose the temporal bulla. Open this and thus reach the 

 tympanic cavity, when the various structures situated in the 

 middle ear are readily brought into view. 



13. Influence of Excitation of one Sense-Organ on the other 

 Sense-Organs. — Urbantschitsch has made a large number of 

 experiments on this subject. 



{a.) Small coloured patches whose shape and colour are not distinctly visible 

 may become so when a tuning-fork is kept vibrating near the ears. In other 

 individuals the visual impressions are diminished by the .same process. 



(b.) On listening to the ticking of a watch, the ticking sounds feebler or 

 stronger on looking at a source of light through glasses of different colours. 



(c.) If the finger be placed in cold or warm water the temperature appears 

 to rise when a red glass is held in front of the eyei. 



