METHODS OF STUDY. 



35 



dried too quickly and were effective for only a few hours. Recourse 

 was had to the proverbial chalk line without success. Bands or 

 ditches of kerosene, crude oil, tar, oils of sassafras and citronella, tree 

 tanglefoot, zenoleum, naphthaline, coal-tar disinfectants, whale-oil 

 soap, sharp-edged tin, and fur were all failures. Certain powerful 

 odors, such as those of zenoleum, sassafras, and citronella, act as 

 repellents temporarily, but after a few hours of evaporation are no 

 longer effective. Ordinarily these ants will not cross bands of cotton 

 tape which have been impregnated with a saturated solution of cor- 

 rosive sublimate and dried, but when attempting to leave an area to 

 which they have been confined by this means they are much more 

 persistent in crossing it. 



Water with a film of whale-oil soap on it acted as a repellent for a 

 few hours only, while a film of kerosene upon water merely afforded 



Fig. 9.— Entrance of artificial formicary shown in figures 7 and 8. (Senior author's illustration.) 



a convenient floor upon which the ants could travel. The difficulty 

 in confining the workers with any liquid or mucilaginous substance 

 lies in the fact that they are exceedingly light,* and sticky substances 

 shortly harden on the sm'face, so that the workers are supported. 

 The surface fihii of clear water is in fact almost strong enough to sup- 

 port a worker not loaded. It is not unusual to see an ant alternately 

 walking and swimming in crossing a narrow ditch of water which has 

 been standing for a few hom-s. Minute dust particles collecting upon 

 standing water shortly form a film upon which the workers pass with 

 ease. Perfectly fresh water therefore served to confine the colonies 

 to their cages, and at first our observations were made upon colonies 

 in cages which were standing in dishes of water. This, however, 

 necessitated frequent changing of the water, and observations were 

 often brought to an abrupt finish by other duties which prevented 

 the change of water in the vessels at the right time. 



1 The average weight of one worker is 0.0002077 gram. 



