CHEMORECEPTION 147 



Morita (1959), recording through the side wall of the chemorecep- 

 tor hair, detected a slow d.c. potential occurring when the tip of the 

 hair was stimulated (Fig. 83). When the stimulus was cither sugar or 

 sodium chloride the potential was negative at the recording point with 

 reference to the base of the hair; when the stimulus was quinine the 

 potential was positive. The closer the recording electrode was placed 

 to the tip of the hair, the greater the negativity when sugar or sodium 

 chloride was applied. On the basis of these recordings Morita has 

 concluded that this slow potential is indeed a generator potential 



%U^> ""'^' 



Fig. 83. A. Response of labellar 

 chemosensory hair of Calliphora 

 to 0-25M sucrose before (top) 

 and after (bottom) crushing. B. 

 Response of a hair to 0-25M 

 sucrose (top), 0-25M sucrose 

 plus 0-05M CaCla (middle), and 

 0-05M CaCla (bottom). Time, 

 -^Q- sec. (Redrawn from Morita 

 and Yamashita, 1959.) 



arising at the point of stimulation and initiating impulses at the base 

 of the hair. He makes no distinction between receptor potential and 

 generator potential, and the presumption is that they are one and the 

 same in this hair. 



The electrical sign of the impulses arising from stimulation proved 

 puzzling, and an attack on this problem threw some light on the 

 question of the site of impulse generation. All workers now agree that 

 the initial component of the spike is positive (Morita et al, 1957; 

 Wolbarsht, 1958 ; Hodgson, 1958 b). Wolbarsht (1958) interpreted this 

 condition as indicating that the distal processes of the chemoreceptive 

 cells act as somewhat poorly insulated extensions of the recording 

 pipette into the interior of the cell. The spikes of the mechano- 



