144 SERGIUS MORGULIS 



is destroyed or injured this particular receptor loses its ability 

 to form conditioned reflexes except by its primitive and general- 

 ized function. Animals whose optic centres have been injured 

 can still form associations between stimuli of various light inten- 

 sities and the salivary reflex, but not with stimuli from special 

 groupings of light and shadow. 



As regards the auditory reactions of the dog it has been dis- 

 covered by the conditioned reflex method (Selionyi. Elliasson, 

 Tichomirov, Babkin, Burmakin) that its auditory faculty is 

 much greater than that of man. The dog perceives J of a tone 

 and appreciates tones of a frequency of vibration which is entirely 

 beyond human reach. It was also discovered that the dog has 

 an absolute memory for sounds, which probably, but very few of 

 the most gifted musicians possess. 



Usiewitch's particular problem has been to study the dog's 

 reaction to an intermittent auditory stimulation with a view to 

 determining its ability to differentiate time intervals. It is 

 hardly necessary to describe his technique, which is essentially 

 the same as already described in the review alluded to. The 

 intermittent stimulation was produced by means of a metronome. 

 The subject of these experiments, a large healthy dog which 

 never had been used for similar tests before, was found to be 

 totally indifferent to the metronome so far as its salivary . reflex 

 was concerned. 



By persistent training a conditioned reflex has been established 

 to the stimulation with 100 oscillations per minute of the metro- 

 nome. The stimulation of intermittent sounds of such frequency 

 called forth 6-10 drops of saliva every time. The interval 

 between successive oscillations was then modified, the moment 

 of the disappearance of the conditioned salivary reflex indicating 

 the lowest limit of differentiation. Without going into any 

 details of this most interesting investigation or quoting actual 

 data, I will say that the dog could sharply distinguish the short- 

 ening of the interval by less than A~A of a second. Indeed 

 with the well developed reflex to the stimulation of 100 beats per 

 minute a change of the rate to either 96 or 104 beats was im- 

 mediately reacted upon by a marked diminution or even complete 

 cessation of the flow of saliva. 



Furthermore, Usiewitch brought out some very significant 

 points with regard to the intermission between tests with the 



