PHYSIOLOGY OF OLFACTION 65 



In these experiments no attempts were made to exclude 

 sight or to ascertain the effects of the operation. In ex- 

 periments carried out by me in 1910 an attempt was 

 made to gain more conclusive evidence. Five normal 

 catfishes (Amiurus) were allowed to swim in an aqua- 

 rium in which were hung two wads of cheese cloth one 

 containing concealed earthworms, and the other made 

 of cloth only. In the course of an hour the wad con- 

 taining the worms was seized eleven times by the fishes 

 notwithstanding the fact that from time to time this wad 

 was interchanged in position with the other. During the 

 same period the wad without worms was passed over by 

 the fishes many times and never excited any noticeable 

 reaction. 



Ten catfishes were next prepared for further experi- 

 mentation ; in five of these the olfactory tracts were cut 

 and from the remaining five the barbels, the seat of the 

 chief external gustatory organs, were removed. After 

 the fishes had recovered from these operations, they were 

 put in an aquarium into which was introduced a wad of 

 cheescloth containing minced earthworms. During the 

 first hour the wad was seized 34 times by fishes without 

 barbels but with normal olfactory organs and, though 

 often passed over by fishes with cut olfactory tracts, it 

 was never seized by any of these and "nosed" only once 

 by one of them. None of these fishes paid any attention 

 to a wad of cloth containing no worms. Repetitions of 

 these tests gave uniformly similar results and led to the 

 conclusion that the olfactory organs of the catfish are 

 serviceable in sensing food at a distance much beyond 

 that at which the organs of taste are capable of acting; 

 in other words, catfishes truly scent their food. 



