12 ZOOLOGY sect. 



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 

 falls to deal out working power so as to cause the movement of the 

 machinery of the clock, so the protoplasm is able, by the degra- 

 dation or decomposition of its complex compounds, to deal out 

 working power enabling the Amoeba to move. In the case of the 

 clock-weight there comes a time when all the potential energy is 

 expended ; the weight reaches its lowest limit, and unless it is 

 wound up again the clock stops. The like holds good of the 

 Amoeba ; the protoplasm is continually being used up — decomposed 

 into compounds of a lower order — and, in course of time, the whole 

 potential energy would become exhausted, were it not that a new 



