GENERAL CONSIDERATIONS 15 



which to grow the chosen form. The most universal of such media, in 

 all probabihty, is the "hay infusion," in which hay in water, preferably 

 after boihng, is allowed to stand for a certain time for bacteria to grow 

 before the protozoon is placed in it. If this is a satisfactory medium, the 

 organism will respond by dividing at a certain rate. After twenty-four 

 hours the culture medium is replaced by fresh medium, made in the 

 same way. In this manner the culture is inaugurated and carried on, and 

 mass cultures are provided and sustained from the reserve individuals that 

 are produced every day. In this manner material is produced for study 

 of individual structures and for various activities characteristic of the 

 different phases of the life cycle. 



In many inaugural cultures made in this way, the outcome is different. 

 No culture is started, or at best a very poor one. The reasons for this 

 are manifold. Usually in such cases the medium turns out to be a suit- 

 able culture medium for some types of organisms, primarily bacteria, 

 which are noxious to the protozoon under study. Hence a knowledge of 

 bacteriological technique is valuable in determining the proper bacterial 

 food to be used (see Kidder, hifra, Chapter VIII). 



A successful culture of a ciliated protozoon, for example, provides 

 ample material for study of structures and functions; for encystment; 

 or for the minutiae of cell division, conjugation, sex phenomena, and the 

 like. The appearance of derived structures of all kinds may be followed 

 in sequence, from their origin in the fundamental organization as it ap- 

 pears in the recently encysted individual, to the active adult. Euplasmatic 

 and alloplasmatic materials and their functional purposes in the cell may 

 be determined, and the investigator proceeds with the confident expecta- 

 tion that plenty of material will be on hand for future study. 



Very often the organism to be studied is carnivorous, and it is neces- 

 sary to provide suitable food material, which must be cultivated for the 

 purpose. Thus Actinobolina radians lives on Halter/a grandmella, 

 Didinium nasutum on Paramecium, and Spathidium spathula on Col- 

 pidium, and practically pure cultures of these food organisms must be 

 kept on hand. For many purposes bacteria-free cultures must be pre- 

 pared, and for this a knowledge of bacteriological technique is not only 

 desirable but essential (see Hall, infra, Chapter IX; Kidder, infra, 

 Chapter VIII). 



