202 H. DIAMANT AND OTHERS 



tissue in the sheath and particularly between the individual fibres when they 

 are situated in a bony canal. This connective tissue makes the nerve 

 mechanically more resistant as it passes between muscles or other movable 

 tissues. Our analyses of the gustatory activity has thus been limited to the 

 study of the integrated response from the entire nerve. 



Even if this restricted our analyses, we have nevertheless obtained a few 

 answers to hitherto unsolved questions. Thus it is obvious that water has 

 no positive action on the gustatory apparatus of man contrary to the case 

 in the rhesus monkey and in the dog and many other mammals except the 

 rat. 



It is of special interest to compare the thresholds as well as the relative 

 gustatory values of different sapid solutions obtained from human chorda 

 tympani records, with the subjective values collected from psychophysical 

 experiments. The close correlation between the threshold values obtained 

 by these different methods is interesting as it shows that even the weakest 

 signalHng registered in the taste fibres is communicated to those parts of 

 the central nervous system which are responsible for conscious perception. 



Although our electrophysiological data are limited to only one case of 

 each species it is interesting to note the difference between responses to 

 alcohol in man and dog. The dog's tongue possesses gustatory receptors 

 for substances that taste sweet in man with the exception of saccharin. It 

 must be remembered that the dog has gustatory receptors responding to 

 water. Thus the absence of response in the dog to weak alcohol solutions 

 (0.5 to 2 m) must be due to a depressing action of alcohol on the receptors 

 responding to water. The delayed response to alcohol in the dog's chorda 

 seems to coincide in its temporal course with the afterdischarge to strong 

 alcohol solutions in the human chorda. 



From our experiments on the dog's chorda it looks as if alcohol pre- 

 ferentially stimulated gustatory nerve fibres which respond to sucrose. Since 

 7 out of 13 of our human subjects reported the alcohol sensation as sweet, 

 it seems likely that the human tongue possesses similar gustatory fibres 

 responding to sweet tasting substances as those described in the dog 

 (Andersson et al. 1950). At higher alcohol concentrations all gustatory 

 nerve fibres may be stimulated in addition to a strong stimulation of tri- 

 geminal nociceptive fibres before the endorgans are paralyzed by the strong 

 alcohol which, of course, belongs to the group of substances which when 

 locally applied produce an anesthesia dolorosa. 



SUMMARY 



1. Integrated electrical responses to sapid substances have been recorded 

 from the tympanic part of the chorda tympani of man during otological 

 operations. 



