SMELL AND TASTE 



1035 



of the labyrinth to which they give rise. Thus, a sound of 100 

 vibrations a second would start 100 impulses a second in the auditory 

 nerve; a loud sound would set up impulses more intense than a 

 feeble sound; and a complex wave, which is the resultant of several 

 sounds of different vibration-frequency, would also in some way or 

 other stamp the impress of its form on the auditory excitation wave ; 

 just as in a telephone every wave in the air causes a swing of the 

 vibrating plate, and thus sets up a current of 

 corresponding intensity and duration in the 

 wires. This theory evidently abandons the 

 doctrine of specific energy for the particular 

 case of the analysis of pitch, for it assumes 

 that differences of auditory sensation are 

 related to differences in the nature of the im- 

 pulses travelling up the auditory nerve, and 

 not merely to differences in the anatomical 

 connections (peripheral and central) of the 

 auditory nerve-fibres. It is unsatisfactory 

 because it takes no account of the remarkable 

 and suggestive structure of the telephone plate 

 i.e., of the organ of Corti and gives no hint 

 of how the analysis is accomplished in the 

 central organ. 



The range of hearing is very great. The 

 highc st audible tone corresponds to 30,000 to 

 40,000 vibrations a second, the lowest to about 

 30. Between these limits as many as 6,000 

 variations of pitch can be perceived. 



Wien has elaborately investigated the question how the sensitive- 

 ness of th e ear varies for tones of different pitch . A tone of 50 vibrations 

 a second, in order to be just heard, must have an intensity corre- 

 sponding to about 100 million times as much energy as is needed for a 

 tone of 2,000 vibrations. It is only on the extraordinary sensibility 

 of the ear for the range of tones used in ordinary speech that the 

 possibility of understanding speech depends when the circumstances 

 are unfavourable e.g., at a great distance, or in the presence of much 

 stronger accompanying noises. 



.,-1 



Fig. 440. Photograph of a 

 Sound- Picture (Ewald). 



SECTION III. SMELL AND TASTE. 



Smell was defined by Kant as ' taste at a distance ' ; and it is 

 obvious that these two senses not only form a natural group when 

 the quality of the sensations is considered, but are closely associated 

 in their physiological action, especially in connection with the 

 perception of the flavour of the food. Their intimate relation is 

 further indicated by the fact that the cortical areas in which smell 

 and taste are represented lie close together or overlap each other 

 on the gyrus hippocampi and uncus (p. 933). The olfactory end- 

 organs in the mucous membrane of the upper part of the nostrils, 

 the so-called regio olfactoria, have been already described (p. 893). 

 In cases of anosmia, in which the olfactory nerve is absent or 

 paralyzed, smell is abolished; but substances such as ammonia and 

 acetic acid, which stimulate the ordinary sensory nerves (nasal 



