ZOOLOGY FOR MEDICAL STUDENTS 



CHAP, 



c.v: 



Sometimes the food-organism is in the form of a long slender thread 

 as is the case with so many of the simpler water weeds or algae. In such 

 a case the Amoeba goes to work in rather a different fashion. Surrounding 

 the filament it spreads along it and gradually draws it inwards so that 

 eventually the filament is coiled up into a mass within the endoplasm. 



Following on the process of ingestion in which it is taken into the body 

 of the Amoeba the food particle undergoes a series of changes. If an 

 actively moving organism its movements are seen to continue for some 

 little time within the food-vacuole but presently they cease and the food- 

 organism is evidently dead. Chemical 

 testing at this stage shows that 

 the watery fluid within the food- 

 vacuole has become strongly acid. 

 Acid has been formed, or secreted as 

 the technical expression is, by the 

 surrounding protoplasm of the 

 Amoeba and poured into the food- 

 vacuole. This acid secretion has 

 apparently for its sole function the 

 killing of the food-organism. 



There now ensues the process of 

 digestion. The green vegetable cell, 

 as we assume the food-organism to be, 

 gradually changes colour becoming 

 dark green, yellow, yellowish red, 

 brown, brownish red. The cellulose 

 wall breaks down and the whole body 

 of the food-organism disintegrates. 

 The protoplasm of the Amoeba 

 has secreted into the food-vacuole 

 digestive ferments. Ferments or enzymes are a remarkable class of 

 substances produced by the living activity of animals or plants, which 

 have the mysterious power (" catalytic " power) of inducing or hurrying 

 up specific chemical changes in substances with which they are in contact. 

 In this particular case the main ferment at work is one which causes 

 the dead protoplasm of the food-organism to break up into simpler 

 chemical compounds which the living substance of the Amoeba is able 

 to absorb and make use of in building up new protoplasm of its own 

 for it appears to be the case that living protoplasm is never able simply 

 to add to itself living protoplasm directly. The latter must be killed and 

 digested, i.e. broken down into simpler substances, before it can be made 



Fig. 3. 



Ingestion of a small animal by an Amoeba. 

 C.V, Contractile vacuole ; /, food-organism 

 in process of ingestion ; /.u, food-vacuole ; 

 H, nucleus. 



