230 RESEARCH IN PROTOZOOLOGY 



pig. This investigator describes both ectoplasmic and endoplasmic 

 structures and especially the neuromotor apparatus. Similar studies 

 are needed of balantidial cysts, and of balantidia from other ani- 

 mals. Certain chromosome-like bodies that are constant in number 

 and size were discovered by Hegner and Holmes (1923) in the 

 macronuclei of balantidia from a Brazilian monkey; this work 

 suggests that a further cytological study of the nuclei of these 

 ciliates would be of value. 



b. Size. Balantidia from different hosts and from a single host 

 vary greatly in size; for example, B. coll from man ranges from 

 30// to 200// or more in length and from 20// to 70// in breadth. 

 Are these variations due to fission and subsequent growth, to the 

 nature of the environment, or are heritably diverse size races or 

 varieties present? Pure line cultures and cross-infection experi- 

 ments would probably answer this question. Rees (1927) was able 

 to obtain a pure line culture of the Balantidium of the pig in one of 

 twelve attempts in the following way : a large drop of culture 

 medium containing a few organisms was spread out on a slide and 

 placed on the stage of a binocular dissecting microscope. Then a 

 single balantidium was sucked up into a fine pipette, and forced 

 out on to a piece of coverglass. This was quickly examined, before 

 it had a chance to dry, so as to be certain that only a single speci- 

 men was present, and then the coverglass, with the balantidium 

 on it, was dropped into a culture tube. Rees reports multiplication, 

 but did not succeed in making a transfer to a second tube. The 

 pipette may be of the ordinary type with a rubber bulb on one 

 end and the other end drawn out in a flame until the diameter is 

 much reduced, or two short pieces of glass tubing may be used, 

 connected by a rubber tube about 6 cm. long, the free end of one 

 tube being sealed and that of the other tube being drawn out fine. 

 This sort of pipette enables one to regulate the suction better than 

 does the type with a bulb at one end. 



c. Specificity. The specific validity of the many balantidia that 

 have been described is somewhat In doubt. A careful study of the 

 entire genus Balautidiuin is desirable from this viewpoint. The 

 structure of specimens from the various hosts needs to be worked 

 out as well as the life-cycles and host-parasite specificity. Con- 

 firmation is needed of McDonald's conclusion that two species of 

 Balantidium live in the pig, B. coli which belongs to the same 

 species as that in man, and B. suis, which is a new species. 



