180 OTTO C. G LASER 



the exit to which the animal had been trained, was closed and one 

 or several of the others were opened. In every case the individuals 

 continued to go to the exit from which they had previously es- 

 caped. Of course this test could not be continued indefinitely, 

 as failure to escape from the tank, resulted in new exploratory 

 movements that in the end led the animals to one of the other 

 openings. Frequent visits to the old corner are characteristic 

 of these secondary trials. 



In another experiment, the association was established amid 

 general noise, so great just above the center of the tank, that 

 probably there were no differences at any of the corners. When 

 the animals, after a brief rest, were placed again in the tank, 

 they were allowed to make their second series of trials in abso- 

 lute silence. In all cases they swam to the right place with no 

 more variation in time or in the complexity of the pathway than 

 is found under ordinary conditions. 



A third test was made by allowing the association to establish 

 itself while a noise was made at one of the other opened escapes. 

 These noises, purposely not loud enough to frighten the animals, 

 but certainly marked enough to be audible, seemed to have no 

 effect whatever. 



SMELL 



To determine the part played by the sense of smell, the exit 

 left open was thoroughly perfumed with cheese. After the asso- 

 ciation was established, the tank was turned in such a way that 

 the perfumed opening was diagonally opposite its original position, 

 whereas another exit, unperfumed, occupied geographically the 

 place previously held by the escape to which the animal had been 

 trained. Variations of this plan, such as holding a piece of cheese, 

 first in one corner, then in another, were also tried, but in each 

 case the animals swam in the direction that led to the earlier 

 escapes. So far as these tests of the importance of smell are con- 

 cerned, they give only negative results. 



