THE GENUS BALANTIDIUM 229 



balantidia from the guinea-pig. A small piece of intestinal wall 

 in a one-half strength Ringer's solution maintained the ciliates and 

 allowed them to multiply by fission. Room temperature (20° C.) 

 was satisfactory and a low oxygen supply and reduced light were 

 found to be favorable. By means of transfers to fresh tubes the 

 balantidia were kept in cultures for from three weeks to one 

 month. 



d. Preparation for study. Living trophozoites and cysts. A 

 sample from the bottom of the intestinal material should be placed 

 on a slide, slightly diluted with normal saline solution, and con- 

 fined under a coverslip. The following characteristics may be de- 

 termined by a study of the living trophozoites : size, shape, length 

 and arrangement of cilia, ectoplasm, endoplasm, peristome, cyto- 

 stome, cytopharynx, cytopyge, contractile vacuoles, food vacuoles 

 (?), nuclei (?), methods of locomotion. The cysts are nearly 

 spherical and within the cyst wall the slowly moving cilia can be 

 seen. 



Stained trophozoites and cysts. Heidenhain's iron-hematoxylin 

 is the most satisfactory stain following fixation in Schaudinn's 

 solution. Eosin, orange G and licht griin may be used as counter 

 stains. Alum cochineal is also satisfactory for general study and 

 Mallory's triple connective tissue stain is good for nuclear dififer- 

 entiation. The surface of the balantidia can be stained by Bress- 

 lau's method (Scott, 1927). A very small drop of a ten per cent 

 solution of China blue is placed on a slide and mixed with a drop 

 of culture medium containing the ciliates. This is allowed to dry 

 slowly at room temperature. During this period particles of the 

 stain are ingested and stain the food vacuoles and ciliary furrows. 

 When dry the preparation is cleared in Xylol and may be mounted 

 in gum dammar or kept uncovered in a dry state. Sections may be 

 made of washed balantidia embedded in paraffin or of the intestinal 

 contents containing balantidia in celloidin. Sections should also be 

 made of invaded tissues when these are available. 



PROBLEMS FOR INVESTIGATION 



I. Morphology and Life-Cycle, a. Structure. Certain purely 

 zoological problems that have come to the attention of the writer 

 are presented here under the heading of Morphology and Life- 

 Cycle. The most detailed account of the structure of any species 

 of Balantidium is that of McDonald (1922) of B. coli from the 



