Sensory Discrimination: The Chemical Sense loi 



found in 1886 that ants of the genus Myrmica whose anten- 

 nae were removed would attack their own nest mates (231). 

 It seems probable that each nest of ants has a peculiar 

 odor which is the basis of the distinction between friends 

 and foes. Bethe tested the smell theory by dipping an 

 ant first in weak alcohol, then in water, and then in the 

 juices obtained by crushing the bodies of a number of ants 

 of another species. He found that an ant thus treated 

 would be attacked and killed by its own nest mates, but 

 could be introduced, though not so easily, into the nest 

 whose odor it now presumably bore, even though its ap- 

 pearance was quite different from that of the ants therein 

 (51). Wasmann repeated these experiments with much 

 less success than Bethe ; bathing Myrmica ants with essence 

 of Tetramorium ant did not preserve them from final de- 

 struction at the jaws of the latter, though it delayed their 

 fate ; nor did much bathing with foreign nest odors induce 

 the ants to attack beetles of the species Lomechusa sirumosa, 

 their accustomed "guests" in the nest, though they seemed 

 disturbed at first. Wasmann apparently thinks other 

 factors besides smell, vision perhaps, enter into the recogni- 

 tion process (762). Bethe, in a later paper, suggests that 

 Wasmann's negative results may have been due , to the 

 fact that the nest smell very quickly returns to the ants 

 after it has been removed ; he himself took account only 

 of the first reaction of other ants toward the one subjected 

 to treatnaent (52)'. Pi6ron (581 a) has repeated Bethe's 

 experiments and confirined his results with eighteen dif- 

 ferent combinations of ant species. Many factors, how- 

 ever, modify the hostile reaction to foreigners. Pi6ron 

 finds that certain species are inclined to be tolerant. At- 

 tacks are more frequent near the nest than at a distance 

 from it. A solitary ant tends to run away rather than to 



