164 life's beginning on the earth 



interacts with the oil or tends to idissolve it. From his 

 vivid description of his experiments we quote the following : 



A drop of oil is mounted on an ordinary glass slide in a mixture of three 

 parts of glycerin with one part of 96 per cent alcohol and covered with a 

 cover glass. The oil and alcohol are miscible, so that a little alcohol is 

 continually passing into the drop of oil, a little of the oil into the alcohol." 

 [The glycerin acts as a neutral medium to prevent a too rapid interaction 

 of the oil and the alcohol.] Such a drop of oil will change its form, send out 

 "pseudopodia," and creep about much as "amoeba" does. At first it may 

 be circular, then a long projection will be sent out on the one side, the entire 

 drop may elongate and progress as a whole in that direction. Currents 

 may be formed within it, "pseudopodia" may extend in several directions 

 at once; at times, the drop may divide — as also happens in Amoeba. Al- 

 together, the drop of oil imitates with some degree of closeness the behavior 

 of Amoeba. 



That a local chemical change taking place within the Amoeba, (produc- 

 ing thus a new substance in a certain area), might cause the formation of a 

 pseudopodium, and movement in a certain direction may be illustrated by 

 introducing some chemically different substance into a certain region of the 

 drop of oil. A very satisfactory method is to inject a little 70 per cent 

 alcohol into the drop near one side. Take up a small drop of the alcohol in a 

 pipette drawn to a very fine point; introduce this beneath the coverglass 

 and into the drop, and press out a very little of the alcohol into the drop, 

 removing the pipette at once. If this is skilfully done, and not too much 

 alcohol is added, the drop will at once send out a "pseudopodium" on the 

 side nearest which the alcohol was introduced, and often follows this up 

 by moving in that direction. Of course, if the alcohol (or any other sub- 

 stance having less surface tension than the oil) could have been produced 

 through a chemical change within the oil, the resulting movement would 

 be the same. 



From these experiments on oil drops, it appears that (he 

 protrusion which resembles a pseudopodium of the Amoeba 

 is (he result of what is termed a lowering of surface tension. 



What is meanl by surface tension? It is a force < (aiding 

 to contract surfaces. But what is meant by ''force," any- 

 way? Well, the much used term "force" is just an ex- 

 pression designating the cause of any action. 



The action witli which we have to deal here is simply the 

 rounding up of the oil to a nearly globe-shaped drop. We 

 may say the drop of oil is acting as though it were con- 



