I AMOEBA 5 



solid surface. Further the coating of slime over the surface of the 

 ectoplasm is apparently also essential to creeping movement. The actual 

 rate of creeping appears to be anything up to about one to three milli- 

 metres in an hour. 



Besides the ordinary fluid vacuoles which may be present in the 

 endoplasm there exists a contractile vacuole. This makes its appearance 

 — ^usually towards the part of the Amoeba which is hindmost when it 

 moves — in the form of a small droplet of water which slowly and regularly 

 increases in size till it is about as large as the nucleus. When it reaches 

 its limit of size it is suddenly obliterated and if the water surrounding 

 the Amoeba contains solid particles, e.g. of indian ink or carmine, these 

 can be seen to be pushed aside, the water of the contractile vacuole 

 passing out to the exterior. Presently a new droplet appears in the 

 position of the vacuole, and this increases and collapses just as before. 

 There goes on in fact a regular rhythm of expansion (diastole) and con- 

 traction (systole) the complete cycle occupying commonly from 5 to 8 

 minutes. The contractile vacuole is constantly pumping water from 

 the protoplasm of the Amoeba to the exterior — water no doubt being 

 absorbed by the general surface of the creature to make good the amount 

 withdrawn. The living protoplasm is thus constantly being flushed 

 with watery fluid by the activities of the contractile vacuole. The 

 purpose of this seems to be mainly in connexion with two great functions 

 of living matter — respiration or breathing and excretion or the getting 

 rid of waste products. The incoming water brings with it supplies of 

 the Oxygen which is essential to all living activity : the outgoing water 

 carries with it the Carbon dioxide and other more complicated waste 

 substances which are constantly being produced by this living activity. 



It is said that the fluid from the contractile vacuole exhibits a curious 

 property outside the body of the Amoeba — that of causing bacteria 

 living in the water to agglutinate or become clumped together in solid 

 masses, and so rendering them more easily taken in by the Amoeba as 

 food. 



The actual process of feeding is difficult to observe for it takes place 

 preferably in the dark or in very faint light. The Amoeba feeds on solid 

 particles of suitable food material such as small plant or animal cells. If 

 the Amoeba comes up to one of these it seems as it were to flow round it 

 (Fig. 3,/) sending out extensions of its protoplasm on all sides of the food 

 particle which meet beyond it and enclose it with a small quantity of 

 the surrounding water. The food particle comes thus to be shut up in 

 a drop of water — the food-vacuole (Fig. 3, f.v) — within the endoplasm 

 of the Amoeba. 



