RELATION OF BURSARIA TO FOOD S 



SO far as I have yet obser\'ed, but a variety of other ciUates, 

 flagellates and rhizpods, it is difficult to find a culture medium 

 which can be readily manipulated, and hence pure line cultures 

 can not be obtained so readily as of a form like Paramecium. 

 The problem of pure line cultivation of this organ sm will not 

 be dealt with in this paper. The material for use in the follow- 

 ing experiments has all been obtained from mixed or 'wild' cul- 

 tures, though the reinoculations from the single parent culture 

 brought into the laboratory seven months ago resulted in a small 

 number of pure lines living side by side in the cultures. 



It is, in fact, preferable in some ways to use material from 

 such wild cultures for the kind of experiments to be considered 

 in this paper. 



Even without the aid of pure cultures or the application of 

 statistical methods to wild cultures it soon became apparent 

 that there are actually at least two very distinct races of Bur- 

 saria which differ in several diverse characters, physiological as 

 well as morphological.^ One form, which under certain food 

 conditions has a tail, has been used exclusively in these experi- 

 ments, since the other form, collected at the same time and 

 lacking a tail, died out early in the experiments. 



I have observed the following organisms to be eaten and di- 

 gested by Bursaria: Chilomonas, Colpidium colpoda, Vorticella 

 and some of its relatives, Oxytricha, Stylonychia, Arcella, Sten- 

 tor, Paramecium, Stephanodiscus, and some kinds of rotifers. 

 Onl}^ once have I observed bacteria to be eaten, and that time 

 in the form of zoogloea. It is, however, certain that bacteria 

 form only a small part, if any, of the usual diet of this organism. 

 The smaller ciliates, flagellates and rhizopods are the favorite 

 article of food. The larger organisms, sudh as Stentor, are sel- 

 dom successfully captured. Paramecium is quite commonly 

 eaten, though Bursaria does not seem to thrive well on this 

 food. Occasionally rotifers are eaten and it was observed on 

 several occasions that these may remain alive within the vacuole 



' I have been unable to find reference in the literature to more than one form 

 of Bursaria. A consideration of the problems connected with the existence of 

 diverse 'races' of Bursaria will be left for a later time. 



