I AMOEBA 7 



use of for building up additional protoplasm for the animal that feeds on 

 it. An important detail to notice in the case of the Amoeba is that the 

 fluid in the food-vacuole when this digestive ferment is at work is found 

 to have lost its acid reaction and to have become distinctly alkaline. In 

 the fact of its working in an alkaline medium the ferment resembles what 

 is known in the higher animals as the tryptic type of digestive ferment. 

 Each type of ferment has an absolutely restricted and specific type of 

 action and it is believed that the breaking up of the cellulose wall of the 

 vegetable cell is brought about by a second ferment quite different from 

 that which digests the protoplasm. 



As the process of digestion goes on the contents of the food-vacuole 

 become completely disintegrated. All that can be made use of for building 

 up new protoplasm is absorbed by the living protoplasm of the Amoeba, 

 and there eventually remain in the vacuole only particles of useless 

 debris — faecal matter. Finally the food-vacuole is seen gradually to 

 approach the surface : it touches the surface film of protoplasm and 

 bursts, and the Amoeba proceeds on its way leaving the little heap of 

 faecal matter behind. 



Before leaving the process of digestion it may be well to accentuate 

 the fact that the killing of the food-organism is an essential preliminary 

 to the process, for it is a remarkable fact that living protoplasm is com- 

 pletely immune to the action of the digestive ferment. Thus the proto- 

 plasmic walls of the food-vacuole though in immediate contact with the 

 digestive ferments are completely unaffected by them, because they are 

 alive.. 



As the Amoeba feeds and keeps on building up new protoplasm it 

 naturally increases in bulk : it grows. Now it is fairly clear that, the 

 organization of Amoeba being what it is, prolonged growth would neces- 

 sarily lead to an impossible state of affairs, for the 7\inoeba must have 

 a sufficiently great area of surface by means of which it can feed and 

 absorb water and oxygen and get rid of waste products. But the more 

 it increases in bulk the smaller in proportion would become its surface, 

 until soon it would be quite inadequate for the animal's needs. Again, 

 the fluid cytoplasm of the Amoeba would obviously lose all cohesion 

 and be quite unable to retain its form were it to be otherwise than of 

 very small dimensions. Consequently there has to exist in nature 

 some corrective to the process of growth which will ensure the Amoeba's 

 not reaching too large a size for efficiency. This corrective is found in 

 the process known as fission, by which the body of the Amoeba becomes 

 nipped across so as to form two individuals. 



The process is inaugurated by the nucleus dividing into two and 



