REACTIONS TO LIGHT IN PLANARIA MACULATA 65 
last was used with the greatest success. A specimen to be 
operated on was placed under a binocular in a flat dish containing 
a layer of paraffin on the bottom. All of the water was then 
‘drawn from the specimen with a small pipette and the animal 
quickly covered with carbonated water from a siphon bottle 
ordinarily used in making carbonated drinks. In twenty to 
thirty seconds the animal thus treated usually becomes motion- 
less. The carbonated water was then drawn off and the specimen 
operated on. As soon as the operation was complete, the plan- 
arian was removed and placed in a numbered aquarium filled 
with fresh spring water, where it was kept for observation. The 
practice of drawing off all of the water just before operating is 
essential, as it causes a secretion of mucus which holds the animal 
fairly fast to the substratum. This mucus adheres more strongly 
to paraffin than to such substances as glass. 
The operations made consist largely of removing eyes, making 
incisions, and cutting off various parts of the body. The in- 
strument used in making these operations consisted of a fine 
knife made by breaking a diagonal piece from a Gillette safety- 
razor blade. This was then placed in a wooden handle and care- 
fully ground on the back to a fine point. With careful manipu- 
lation one can run such a knife under the eye of a planarian and 
remove it without appreciably disturbing any of the surrounding 
tissue. Parts of an eye can even be removed without destroying 
the capacity to function of the remainder of the organ. 
In making delicate operations upon planarians it was soon 
recognized that there was no way of accurately estimating the 
injury from the operation in the living specimen. For this 
reason each animal, after being experimented upon, was care- 
fully fixed and sectioned to ascertain the extent of the injury to 
the various organs. In this as well as in the general histological 
work several fixing fluids were used, such as Flemming’s stronger 
solution, Bouin’s fluid, Worcester’s fluid, and various corrosive- 
sublimate mixtures. In practically all cases, however, the best 
results were obtained with a chromo-aceto-formalin mixture used 
by Kepner and Taliaferro (716) in working with Rhabdocoeles. 
One very desirable characteristic of this fluid is that it kills so 
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