ON THE FEEDING HABITS OF AMEBA 549 



The food vacuole 



After the food cup closes up completely it is known as a food 

 vacuole. If the food particle is an active organism the food 

 vacuole ordinarily remains undiminished or decreases but very 

 slowly in size until the organism stops moving. At this time or 

 soon thereafter, the water rapidly disappears while small irreg- 

 ular projections are thrown out from the inside wall of the vacuole 

 toward the food. This process may be regarded as a change of 

 the ectoplasm lining the vacuole, to endoplasm, which now fills 

 up most of the space occupied by the water, according to the sug- 

 gestion first advanced by Wallich ('63). The time required by 

 amebas to kill living prey varies greatly. A hungry ameba kills 

 a chilomonas in a minute or less and a coleps in two to five min- 

 utes while a very granular ameba was observed to contain a live 

 flagellate about six microns in diameter in a vacuole for over an 

 hour. I suspect that this ameba was sick, and that its digestive 

 apparatus was disordered. If there is no solid object in the 

 vacuole the water may remain much longer, an hour or more, 

 without any marked diminution in size of the vacuole. 



When the water of a food vacuole containing solid food dis- 

 appears, the food particle is usually carried near the posterior 

 part of the animal, especially if the object is ten microns or more 

 in diameter. After some time, depending perhaps upon its 

 nature, the food particle may be carried along by the main 

 stream of protoplasm. Foods which are only slowl}^ broken up 

 by the digestive powers of the ameba, such as globulin, grain 

 gluten, etc., may be carried for three or four days. A fragment 

 of aelosoma meat may likewise be carried for several days, under- 

 going the while gradual reduction in size. 



On the other hand, diatoms and desmids have been observed 

 to be thrown out occasionally, a few hours after eating, without 

 apparent reference to the degree of digestion. If the ingested 

 substances are indigestible, such as carmine or glass, thej^ are 

 usually thrown out within a few minutes after they are taken in; 

 but in a few cases carmine was carried around for over four hours. 



