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, 1 and sticky substances 
shortly harden on the surface, so that the workers are supported. 
The surface film 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 hours. 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. 
