and Laboratory Methods. 1599 



of great importance not to add too much alcohol ; if this is done, the drop will 

 " explode " and dissolve in place of sending out a projection. 



The movements of Amoeba are of course largely controlled by external con- 

 ditions. That this power of responding to external changes by directed move- 

 ment is by no means peculiar to protoplasm or to living things, may be well 

 illustrated with the drop of clove oil. Amoeba regulates its movements according 

 to the chemical substances present in the surrounding medium, moving towards 

 some, away from others. The same is true for the drop of clove oil. If a drop 

 of weak alcohol is introduced with the capillary pipette near to the clove oil, the 

 latter will at once send out a " pseudopodium " in that direction, and will usually 

 follow this up by moving as a whole toward the alcohol. Amoeba regulates its 

 movements with reference to the comparative temperature of different parts of 

 the region where it is found. This also is true for the drop of clove oil. If a 

 small portion of the slide is heated, as by holding the end of a hot wire against 

 the cover-glass near to the drop of oil, the latter will send out a " pseudopodium " 

 and begin to travel in the direction of the heated spot. 



In injecting the alcohol, it is important not to inject too much, and to bring 

 it very near to the drop of oil. For the movements toward a heated region, make 

 a loop or ball at the end of a small wire ; heat this hot in the flame of an alcohol 

 lamp, then touch the cover-glass not far from the drop of clove oil. The wire 

 must be still very hot when it touches the cover. For all these experiments, use 

 freshly mounted active drops. 



3. Choice of Food. One of the most striking phenomena in the behavior of 

 Amoeba is its power of selecting substances which shall serve as food. Amoeba 

 takes its food simply by sending out pseudopodia, flowing around, and envelop- 

 ing small bodies. But it by no means takes these at random ; sand, decayed 

 plant tissue, bits of wood, dirt, etc., are as a rule rejected, while small living 

 plant and animal cells, diatoms, infusoria, are enveloped, carried away, and 

 digested. It thus shows a distinct choice in the substances which it takes into 

 itself, and the power of choice has often been considered evidence of a rather 

 highly developed mind. 



Before accepting this conclusion for Amoeba, it will be wise to test this mat- 

 ter of the power of choice for other fluids. A drop of chloroform is a good 

 subject for experimentation. With a medicine dropper a drop of chloroform may 

 be placed in the bottom of a watch-glass of water, and then with fine tweezers 

 we may offer it various substances to test its power of choice. The whole pro- 

 ceeding may seem at first thought very absurd, but the results are striking. 



We may first offer the drop of chloroform a fragment of glass ; this is held 

 with the tweezers against the surface of the drop. It is not accepted. We push 

 the glass against the drop, but the latter withdraws its surface from it so far as 

 possible. We force the bit of glass into the drop of chloroform and let go of it. 

 It is at once thrown out with energy. We try a small piece of wood in the same 

 way ; it is rejected as decidedly as was the glass. We may now try a hard piece 

 of gum shellac. This is accepted, — eagerly, one had almost said. Hardly has 

 an angle of the piece of shellac touched the surface of the drop, when the latter 

 literally reaches out, envelops the shellac, and draws it into itself. If we take 



