176 NA TURE STUD Y RE VIE W [9 :6— Sept. , 1913 



It follows that a difference in behavior of the animals in the two 

 vessels must be due to the experimental factor. 



The general conditions in both experiment and control should 

 be sufficiently like the natural environment to permit the animals 

 to behave normally. Granite ware pans are satisfactory and 

 inexpensive as containers for animals during experimentation and 

 they are not aft'ected by the water. However, the bottom is often 

 too slippery to allow the animals to react readily; when this is 

 the case it should be covered with a layer of beeswax. Sometimes 

 the comers will need to be rounded out with the wax to prevent 

 the animals from collecting in them. For most of the experiments 

 outlined in this paper narrow granite iron bread pans are entirely 

 adequate, and the black paper in which photographic supplies 

 are packed may be used whenever black paper is required. 



Unless otherwise indicated, one inch of water should be placed 

 in the pans for each experiment. Whenever possible the water 

 should be taken from the container in which the animals are kept. 

 If other water is used it must be approximately the same tempera- 

 ture as that in which the animals are living. If tap water is used 

 it must be allowed to stand long enough for the gases with which it 

 is supersaturated to escape. It is sometimes preferable to allow 

 the water to stand over night in order that it inay be perfectly 

 free from bubbles. If the water is not allowed to come to air 

 saturation the air bubbles often collect on the appendages of the 

 animal being tested and interfere seriously with its reaction. 



Whenever possible animals should be handled with the bare 

 fingers as they are less apt to be crushed than when other methods 

 are employed. When this is impracticable ordinary tweezers 

 with the ends wrapped with soft cloth may be used to advantage ; 

 bare tweezers are apt to inflict injury. Small animals may also 

 be handled with a section lifter or a common spoon. 



Phototaxis. 



I. Purpose. — To determine whether animals are positive or 

 negative to white light of a given intensity. 



Materials. — Two granite iron bread pans of equal size; black 

 paper. 



Procedure. — Put one inch of water in each pan and place in each 

 an equal ntimber of the animals to be tested. Stir the animals 

 until they are equally scattered over the pans. Cover one pan 



