66 W. H. TALIAFERRO 
rapidly that no anesthetic is necessary to obtain animals fixed 
free from contortions. In the general histological work iron 
haematoxylin with Bordeaux red, and Mallory’s connective-tissue 
stain were used. For ascertaining the amount of injury due to 
the operations, by far the most useful was Mallory’s connective- 
tissue stain. For general purposes this stain was used almost 
exclusively. 
The apparatus used for observing the orientation of animals in 
a horizontal beam of light was essentially like that used by Mast 
(11) and a number of other investigators (fig. 1). The apparatus 
was so constructed that two horizontal beams of light inter- 
sected at right angles in the aquarium in which the observations: 
were made. Either beam could be eliminated and the one 
eliminated could be changed almost instantly by means of a 
double-throw switch (fig. 1, A). Each beam of light was produced 
by a 125-watt gas-filled lamp (fig. 1, 2) which was housed in a 
well-ventilated, light-tight box and properly screened. Each of 
these boxes was placed on a graduated track along which they 
could be moved. The distance of the light source and hence the 
intensity of illumination could thus be varied at will. Each 
beam of light after leaving the aperture in its box was passed 
through distilled water (25 mm.) to remove the heat-waves, and 
was then so screened as to permit practically nothing but parallel 
rays to strike the animals (fig. 1). The heat-waves were of course 
further absorbed by passing through the water of the aquarium 
in which the animals were placed. The stand on which the 
aquarium rested was of the same height as a microscope stage, 
so that in carefully observing the path of ananimal a microscope 
with a camera-lucida attachment could be substituted for the 
stand. When a microscope with a camera lucida was used, a 
small drawing-board was placed beside the microscope (fig. 1, C.), 
and illuminated by a small light which was so secured that no 
light could strike the animals under observation. In tracing 
the paths of specimens with a microscope and camera lucida, it 
was found advisable to use very low magnifications. The use of 
very low objectives (4 inch) and eyepieces not only permitted 
the observation of specimens over a greater range, but it also 
