CANNIBALISM IN AMOEBA 703 



of the culture dishes with a pipette, and must, therefore, have 

 been extruded in the cuU.ures where the stimuhis of strong 

 hght did not operate. Drying of the shde might conceivably 

 have caused extrusion, as Wallich also suggested (29). But 

 this factor also would not operate either in the cultures or in 

 the preparations used for observing living specimens. 



To return to the question of what caused the amoebae to 



become cannibahstic, I am unable to offer any intelligent 



suggestion. It has already been mentioned that the cultures 



were not unhealthy, since the amoebae throve and multiplied, 



as did also the Ciliates and other small amoebae. The balance 



of evidence showed that the amoebae were not to be regarded 



as starved, and certainly not as so starved that they resorted 



to utilizing their own kind as food, a condition which must 



be rare in both natural and artificial conditions. Further, 



we have seen that it is at least very doubtful that they were 



really feeding at all on the amoebae which they ingested, since 



the evidence is that they could only very occasionally digest 



them. Their condition seems to have been like that of the army 



recruit, who, when he asked for a drink on the march, was told 



to suck a stone. 



A possible explanation may be sought in the view that the 

 amoebae had become so numerous in the cultures that the 

 active ones were ingesting the rounded ones and, finding them 

 indigestible, were extruding them again. Schaeffer's work on 

 the feeding habits of amoebae (23) is interesting in this con- 

 nexion. He found that the ingestion of particles by amoebae 

 is not to be explained entirely by chemotaxis, but that other 

 factors operate, especially movement, either natural or mechani- 

 cal, in the material offered, the nature of the amoeba itself, 

 i. e. whether it were ' raptorial ' or not, the physical similarity 

 to or difference from the normal diet of the material offered 

 and the degree of hunger from which the amoebae were suffer- 

 ing. He found, for example, in his experiments with carmine 

 grains, that the amoebae got rid of these much more quickly 

 than normal food matter, and generally as soon as possible. 



Also he thought that the carmine was extruded because it was 



3b2 



