THE GENUS BALANTIDIUM 227 



Guinea-pig. Balantidia may also be obtained from guinea-pigs, 

 in which they occur in the cecum and upper colon in the tropho- 

 zoite stage and in these locations and in the lower colon in the cyst 

 stage. Cysts appear to be common in the more solid fecal pellets. 

 The balantidia in the cecum of the guinea-pig seem shorter and 

 broader than those in the pig, but this is probably due to the nature 

 of the environment, since they resemble the latter when both types 

 are grown in the same culture medium. 



Monkeys, man, etc. In certain localities balantidia may be ob- 

 tained from monkeys and man (especially in certain tropical coun- 

 tries) or from frogs or insects, but pigs and guinea-pigs are the 

 best sources of supply. 



b. Viahility tinder laboratory conditions. That trophozoites of 

 B. coli are very resistant to cooling is indicated by the work 

 of Rees (1927) who noted that at room temperature (about 

 20° C. = 68° F. ) the organisms remain active and apparently 

 normal for from four to eleven days; other workers (McDonald, 

 1922; Jameson, 1927) state that these ciHates die within a few 

 hours when brought into the laboratory. It is probably always best 

 to use fresh material for study or else to grow the ciliates in cul- 

 ture media. Specimens are more numerous at the bottom of the 

 fecal mass, probably because they are anaerobic or react positively 

 to gravity. 



c. Cultivation. B. coli from man was first cultivated by Barret 

 and Yarbrough (1921) and later by van der Reis (1923). The 

 medium of Barret and Yarbrough consisted of one part of inacti- 

 vated human blood serum to sixteen parts of 0.5% salt solution. 

 About 0.1 of a cubic centimeter of undiluted feces was placed at 

 the bottom of tubes ten millimeters in diameter and 150 mm. in 

 length containing about eight cubic centimeters of the medium; 

 they were then incubated at 37° C. Maximum growth took place 

 in from forty-eight to seventy-two hours and subcultures were 

 inoculated every second day over a period of thirty-two days, 

 when the cultures were allowed to die out. Cysts were present in 

 some of the cultures ; binary fission was common ; and w^hat 

 appeared to be conjugation was observed on one occasion. 



A similar medium to that described above was used by Rees 

 (1927) in his work with B. coli from the pig. A modification of a 

 Ringer's solution (NaCl 6.5 gms., KCl 0.14 gm., CaCL 0.12 gm., 

 NaHCOs 0.20 gm., and Na2HP04 o.oi gm., per liter of distilled 



