16 HARRY MILES JOHNSON 



apparatus is subject to several gross defects which had been 

 eliminated in color-vision tests on animals made by Yerkes some 

 years before Kalischer's work was published, by the use of the 

 food-stimulus method. 



The auditory tests reported in this article were carried on 

 by the same method as was employed in the earlier work, except 

 that some animals were trained to respond to as many as three 

 (single) food-tones — high, middle and deep. Different animals 

 responded to tones from Fj to f^ sounded on the harmonium. 

 Kalischer says that in the beginning of this experiment when 

 the food-tone was sounded he helped the animals perform their 

 reactions; but that later they performed them voluntarily 

 "without any help being given." Most of the animals had 

 already been trained to react to one food-tone, and Kalischer 

 tells us that the training had to be continued long enough for 

 the new food-tone to become "fixed in memory" before reac- 

 tion became sure. How long a time was required he does not say. 



After the animals had been trained to two food-tones, one 

 high and the other deep, one labyrinth was completely de- 

 stroyed, making the animal wholly deaf on that side. The 

 method used was the mastoid opening of Heidenhain. Destruc- 

 tion of both cochlea and vestibular apparatus was made com- 

 plete. Training was continued for two or three weeks after 

 the operation, which had not damaged the dogs' accuracy in 

 discrimination. By the same method the second cochlea was 

 then exposed, and the part of the cochlea desired was removed 

 by first piercing the "knee-capsule" covering the cochlea with 

 a fine drill-point, and removing the parts with a needle. One 

 animal in particular, trained before the operation to respond 

 only to food-tones Ai and c^ suffered no loss of accuracy in dis- 

 criminating between these tones and all others. Post mortem 

 showed entire destruction of one cochlea, and removal of the 

 other as far down as the lowest turn. Only this small portion 

 of the cochlea and the vestibular apparatus were left intact. 

 The part of the organ of Corti and of the membrane of Reissner 

 contained in this part of the cochlea, and also the cells of the 

 spiral ganglion which belong to this turn of the cochlea, were 

 uninjured. Reaction to the spoken words "Seeks" and '' Drei" 

 was also perfect, the animal being allowed to take food when 

 they were spoken. 



