ELECTROPHYSIOLOGICAL STUDIES 195 



free access to the cavum tympani. In the majority of cases it was fairly 

 easy to dissect the chorda tympani free from the surrounding bony struc- 

 tures but in some cases the chorda was completely covered by bone and 

 had to be ground free. In general, such cases gave poor results as the 

 chorda tympani has a more gelatinous structure when inside a bony 

 channel than when it is outside and surrounded by connective tissue. For 

 that reason it also proved futile to split up the nerve into small strands for 

 single fibre recordings. Bleeding during the operation was stopped by 

 applying pure adrenaline solution without any anaesthetic addition. The 

 chorda was cut centrally as near as possible to the point where it comes 

 out from the 7th nerve canal. The sheath was removed leaving a naked 

 nerve trunk for a length of 3-5 mm which could be put on the electrode. 



In the beginning we used a double platinum electrode which was fixed 

 on the ear speculum but later we found it more convenient to use a single 

 electrode. The electrical response was recorded by means of an r.c- 

 coupled amplifier and a two channel tape recorder (Tandberg stereo). Thus 

 the electrical response from the nerve, the signals and the minutes of the 

 experiment were simultaneously recorded. After the actual experiment the 

 tape records were processed in the laboratory by means of an integrator 

 and a cathode ray oscillograph or an ink-writer (Mingograf) producing the 

 integrated records of the electrical responses. 



Sapid substances were applied to the tongue by means of a special dis- 

 pensing device fixed in position with its tip approximately 3 mm above the 

 tongue. To the stopcock a switch was attached which gave a signal on the 

 record when the test solution (15 ml at 30'C) was released. The tongue as 

 well as the burette was rinsed with 30 C water before each trial. 



RESULTS 



In eight out of 32 patients tested we did not obtain any response what- 

 ever from the chorda tympani. In another seven cases the response was very 

 poor or electrical disturbances occurred. Thus there remained 17 cases in 

 which the records were good enough to be analyzed further. 



As is the case in other mammals, the human chorda responded to 

 mechanical and cold stimulation of the tongue, and the mechanical response 

 was comparatively weak, which implies that only a few mechanoceptive 

 fibres run via the chorda tympani. Warm water 37-43'C generally gave 

 no response while cold water gave very pronounced responses. None of 

 the chordas tested responded positively to the application of distilled 

 water of the same temperature as the surface of the tongue. 



Response to NaCl 



Positive responses to NaCl solutions were obtained in all the successful 

 experiments and in six cases we obtained a complete series of responses to 



