76 Asa Arthur Schaeffer 



tion of insoluble material is readily observed in many of these 

 organisms, and this fact together with the generalh accepted 

 notion that the protozoa are much simpler organisms than the 

 recent work shows them to be, was perhaps largely responsible for 

 thinking the selection of food a question answerable by more or 

 less casual observation and by inference from the general behavior. 

 This is brought out by comparing the views of some of the more 

 important workers. 



Prior to Verworn's work, which may be regarded as the point of 

 departure for the recent interest in the protozoa, the consensus of 

 opinion of workers in this field seems to have declared in favor of 

 the abilitv of these organisms to ingest certain kinds of particles 

 and to reject certain other kinds in a systematic manner. Thus 

 Stein ('67) and Entz ('88) and others declared unequivocally that 

 in in fusoria, whenever " foreign " particles were brought by the " ali- 

 mentary vortex" into the "pharynx," the current was stopped or 

 given such a direction that the foreign particle was swept away. 

 Neither of these writers, however, seems to have taken into 

 account nor tried to explain the earlier observations of Ehrenberg 

 ('38) and others, who described the ingestion by certain infusoria 

 of large quantities of carmine grains, which can hardly be regarded 

 as anything but "foreign" particles. 



Verworn ('89) took up this question and confirmed Ehrenberg's 

 results with carmine; he also observed that chalk crystals, indigo 

 particles, and the like, were freely mgested. At the same time 

 that these indigestible particles were swallowed, small organisms 

 such as swarm spores and micrococci were often swept away by the 

 cilia. From these and other observations Verworn concluded 

 that there is no selection obtaining among the various kinds of 

 particles which the alimentary vortex brings to the mouth of the 

 infusorian. 



Biitschli ('89) also came to the conclusion that the power of 

 choice of food is absent in the protozoa. 



But in 1893 ^^ opposite view was again advanced by Hodge 

 and Aikins, who said that "a prine condition of the creature's 

 (Vorticella) life must be its ability to distinguish food from what is 

 not food." But there is no reference to or explanation of either 



