CHEMORECEPTION 143 



and Kuwabara (1957) independently developed a novel technique. It 

 consisted of placing a fluid-filled micropipette over the tip of a hair 

 and employing it both as a recording electrode and as a source of 

 chemical stimulation. More recently a greatly improved technique was 

 developed by Morita (1959). It involved puncturing the side wall of the 

 hair and recording with the pipette electrode from this point. The tip 

 of the hair was thus left free for stimulation by any kind of material 

 whether electrolyte or not. The indifferent electrode was inserted into 

 the crushed head. 



Originally the potentials from only two neurons were recognized in 

 the records obtained from the fly (Hodgson et al. 1955; Hodgson and 

 Roeder, 1956). One neuron, designated the L (for large spike) fibre by 



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Fig. 82. Electrical response of a labellar hair ofPhormia to stimulation by 

 salt, sucrose, and bending. A, intact hair stimulated with 0-01 M NaCl 

 and motion. B, same hair with tip removed. C, cut hair stimulated by 

 OOIM NaCl + O-IM i)-fructose. The hair is bent at arrow. D, same 

 hair responding to motion after adaptation to chemicals. Time, 0-2 sec. 

 Positive potential at recording electrode is down. (From Wolbarsht 

 and Dethier, 1958.) 



Hodgson and Roeder (1956), clearly responded to salts, while the 

 other, designated as the S (for small spike) fibre, responded to sugars. 

 Subsequently, Wolbarsht and Dethier (1958) were able to detect the 

 spikes of a third neuron (designated M for mechanoreceptor) which 

 responded only to bending of the hair (Fig. 82). Mellon and Evans 

 (1961) have now detected spikes from a fourth neuron which responds 

 to water. The function of the fifth neuron, present in some hairs, is not 

 known. 



Since it is now known that certain hairs contain four distinct re- 

 ceptors, conclusions drawn from earlier studies of electrophysiological 

 records must be re-evaluated, specifically the conclusions that: low 

 concentrations of salt sometimes stimulate both L and S fibres 

 (Hodgson and Roeder, 1956), that acids and alcohols stimulate the L 

 fibre (Hodgson and Roeder, 1956), that water stimulates L and 5 fibres 



