494 | The American Naturalist. [May, 
diluted with an equal bulk of water, and the drops will then exhibit a 
vigorous streaming and forward movement, becoming gradually trans- 
parent. The amceboid movements are generally more distinct if the 
drops are somewhat compressed. If the drops do not show the stream- 
ing movement. you may succeed in producing it by tapping the cover- 
glass slightly, by applying gentle pressure, or sometimes by breaking 
up the drops. For it seems as if at times incrustations were formed on 
the surface of the drops which prevent or impede the streaming move- 
ment, and which can, in part at least, be removed by the above- 
mentioned manipulations. 
It is especially interesting to see how fast and beautifully the drops 
creep to and fro in water, or in half-diluted glycerine, even when they 
are not compressed. The streaming movement, on the other hand, is 
better seen if the drops are compressed, which may be done by insert- 
ing under the cover-glass a piece of broken cover-glass of medium 
thickness, and then removing the paraffine pegs. Then draw away the 
liquid until the necessary pressure is obtained. This streaming move- 
ment is better demonstrated twenty-four hours after the addition of the 
glycerine, as the drops will then be thoroughly cleared and transparent. 
Further, it is interesting to note that a Progression of the drops takes 
place in the direction in which the streaming moves. 
As this forward movement is rather slow in compressed drops, it is 
necessary to use a micrometer ocular to satisfy one’s self of the advance. 
Unfortunately the oils which I have prepared since my first experi- 
ments do not move and stream so well or so rapidly as those I employed 
then. The movement and streamirg show themselves much more 
markedly and distinctly if they are examined on a warmed stage at a 
temperature of 50° C. If you should be in a position at your demon- 
strations to conduct the experiment at this temperature, the phenomena 
will certainly be much more evident. 
From the preceding description you will see that it will be necessary, 
to obtain %ood results, to gradually get hold of the methods, and you 
must not doubt the correctness of the. phenomena which I have described 
if the first trials do not give the desired results. 
At all events, you will have at first to make some experiments so 
as to obtain an insight into the conditions and sort of phenomena, 
but I do not doubt that you will succeed in observing the appearances 
and in demonstrating them to others, though perhaps in not so vigorous 
a degree as I might desire, 
I have lately made some other trials to render olive oil suitable for 
these experiments by heating it more rapidly. Although at present I 

