THE GENUS BALANTIDIUM 231 



Measurements of conjugants, exconjugants, and recently divided 

 specimens should be made to aid in determining this point. Pure 

 line cultures started with co/i-like and suis-Xikt specimens respec- 

 tively might settle the question. Confirmation is also needed of 

 Scott's assertion that the balantidia of the guinea-pig are specifi- 

 cally identical with B. coli of man. 



d. Fission. Binary fission has been observed frequently in mate- 

 rial taken directly from animals as well as in specimens grown in 

 culture media, but the details of the process have been described 

 only in a general way (Scott, 1927) and in a limited number of 

 species. 



e. Conjugation. Scott (1927) and Jameson (1927) have re- 

 cently published data on conjugation in balantidia from the guinea- 

 pig and pig respectively, but much work still needs to be done with 

 these types as well as with balantidia from other animals. Conjuga- 

 tion took place in Jameson's cultures periodically, the intervals 

 observed being in some cases three days and in others one w^eek, 

 but the conjugants did not encyst as described by Brumpt (1909). 

 Do conjugation cysts actually occur? What factors induce con- 

 jugation? Is conjugation usually periodic? 



f. Budding and Sporulation. Does budding occur, as described 

 by several investigators (for example, Ohi, 1924) and sporula- 

 tion (Walker, 1913) ? 



2. Host-Parasite Relations, a. Transmission. Data on the via- 

 bility of trophozoites of B. coli when outside of the host are con- 

 tradictory (McDonald, Rees). A series of experiments might well 

 be undertaken to determine the factors involved, and their eft'ects 

 on trophozoites and cysts. It is generally supposed that man be- 

 comes infected by swallowing cysts from pigs ; the truth of this 

 supposition should be determined experimentally. Are trophozoites 

 infective? Hegner (1926) found that trophozoites from the pig 

 would pass through the stomach and small intestine (120 cm.) of 

 the guinea-pig and reach the cecum in a viable condition within 

 one hour; this was confirmed by Rees. It is still to be learned 

 whether or not trophozoites are able to reach the colon of larger 

 animals, such as the pig and man, alive. The conditions that exist 

 within the digestive tract might be simulated in the laboratory and 

 the ciliates subjected to them, especially in cultures. The effects of 

 treating balantidia both in pigs' feces and in culture with hydrogen 

 sulphide have been studied by Rees but with variable results. 



