452 STELLA B. VINCENT 



A 512 c' fork was used for the tone stimulus and the alternate 

 noise stimulus was hand clapping. The animals were to go to 

 the right or to the left respectively at the stimulus. Under 

 the conditions the errors steadily decreased but when the tone 

 was withheld the reaction remained the same proving that the 

 animals were reacting to noise only. None of seven rats in 700 

 trials learned to react to tone. There was also failure to dis- 

 criminate between different intensities of c'. Many noises were 

 substituted successfully for hand clapping with another set of 

 animals. Interrupted tones gave no better results. The author 

 concludes that either the rats cannot hear c' or that their sen- 

 sitivity to this tone is extremely slight. 



OLFACTION AND CHEMICAL SENSITIVITY 



Mammals. — A note on the supposed hunting response of the 

 dog by Johnson (15) is a brief but interesting bit of analysis 

 of some of the theories adduced to account for the ability of 

 the dog to trail his master or track his prey. 



Amphibians. — Risser (27) studied the toad in its reactions to 

 natural or artificial food odor in living or dead animals. Odor 

 streams were tried and the experiments were repeated in dark- 

 ness. The species used was Bnfo americanus Le Conte. His 

 conclusions are that the visual is the sole stimulus which arouses 

 the food response of the toad and that this is effective only when 

 the food is in motion. Rejection of food, he thinks, is due to 

 mechanical or tactual stimulation and the gustatory function 

 is negligible. No positive conclusions are drawn as to olfaction 

 yet he found it difficult to establish any connection between the 

 seeking of food and inherent food odors. Odor streams caused 

 definite motor activities which were proven by operative pro- 

 cedure to have an olfactory stimulus. The reactions which 

 were inhibited by section of the olfactory tract were not affected 

 by section of the trigeminal nerve. Tadpoles appear to use 

 olfaction in discrimination of foods. The author says, "In the 

 metamorphosed toad the visual stimulus is the principal and 

 guiding factor in procuring food. Therefore it is inhibitory in 

 relation to other stimuli and their resultant reactions." 



Rapid modification of behavior was noted by Shelford (30) 

 in experiments designed to test the sensibility of amphibians to 



