12 ZOOLOGY SECT. 



When this is watched it will be observed to increase gradually 

 in size till it reaches a maximum of, let us say, a fifth of the 

 total diameter of the Amoeba, when, by a contraction of its walls, 

 it suddenly disappears, to reappear presently and gradually grow 

 again to its maximum size. This pulsating clear space is the 

 contractile vacuole. Other clear spaces which do not pulsate are 

 the non-contractile vacuoles. 



By watching the Amoeba carefully for some time we may be 

 enabled to observe that the movements of the protoplasm of the 

 body not only effect locomotion, but are connected also with the 

 reception of certain foreign particles of organic nature i.e. either 

 entire minute animals or plants, or minute fragments of larger 

 forms into the interior of the protoplasm. A process of the 

 protoplasm is pressed against such a particle, which becomes sunk 

 in the soft substance, and passes gradually into the interior. Here 

 it becomes enclosed in one of the non-contractile vacuoles, and by 

 degrees partially or wholly disappears ; the part, if any, which 

 remains subsequently passes outwards from the protoplasm into 

 the surrounding water. The matter which disappears evidently 

 mixes with the protoplasm and adds to its bulk. All, in fact, of 

 the matter of the foreign body that is capable of doing so, becomes 

 digested and assimilated by the protoplasm. The fluid in the 

 vacuole enclosing the food-particle (for such is the true nature of the 

 foreign body) probably contains some ingredient of the nature of a 

 ferment, which is able to act on certain substances and render 

 them more soluble or capable of being more readily taken up by 

 the protoplasm. This we infer mainly from what we know of the 

 digestion and absorption of food in the higher animals ; but the 

 fact, which has been established by experiment, that the Amoeba 

 is able readily to digest certain classes of organic substances, while 

 others, when taken into the interior of the protoplasm, remain 

 unaltered, seems to indicate that some special property, similar to 

 those possessed by the digestive ferments of the higher animals, 

 is present in the watery fluid surrounding the food-particle. 



The movements of the Amoeba, slow and gradual though they 

 are, must involve a certain expenditure of energy or working power ; 

 this can only be derived from the energy of chemical affinity 

 which the protoplasm possesses in virtue of its complex chemical 

 composition. The protoplasm loses some of this energy by its 

 conversion into energy of movement. This loss implies the break- 

 ing up of the complex chemical ingredients of which protoplasm 

 is composed into simpler ones ; the protoplasm falls a grade in 

 the scale of chemical compounds, and by its fall generates the 

 force by means of which the Amoeba moves. The energy of 

 chemical affinity which the protoplasm possesses is thus analogous 

 to the potential energy which the weight of a clock has when it is 

 wound up. As the weight, by virtue of its position, is able as it 



