THE CULTIVATION OF INTESTINAL PROTOZOA 71 



Balantidiuui coli was first cultivated by Barret and Yarbrough 

 (1921) using a medium composed of one part of human serum 

 plus sixteen parts of 0.5% sodium chloride solution. The 

 balantidia multiplied over a period of thirty-two days, eleven 

 transplants being made. Recently Rees (1927) has successfully 

 cultivated balantidia from the pig and guinea-pig using a modi- 

 fication of the medium of Barret and Yarbrough. Rees substituted 

 Ringer's solution without dextrose for the sodium chloride solu- 

 tion and added a minute amount of rice starch. 



PROBLEMS FOR FUTURE WORK 



Protozoology, in all its numerous phases, presents a vast field 

 for research. Of the many problems suggesting themselves in the 

 particular field of this chapter, a few are here mentioned : 



(i) Obtaining pure cultures of the various protozoa. Qeve- 

 land's work (1928) along this line is notable. Several problems 

 present themselves in this particular field. First, is the obtaining 

 of pure line cultures, or cultures from single organisms. Second, 

 the isolation of pure line cultures and their cultivation with a 

 single known species of bacteria. Third, the isolation of pure line 

 cultures and their cultivation with a single known species of dead 

 bacteria. Fourth, the isolation of a pure line culture free from 

 all bacteria. 



(2) Infection experiments with pure cultures. This problem 

 would be dependent upon, to a certain extent, the problems pre- 

 viously mentioned. After obtaining any of the so-called pure cul- 

 tures above mentioned, the next step would be the infection of 

 protozoa-free animals with these cultures, with a view to deter- 

 mining (a) methods of infection, length of incubation time, length 

 of infection, and the effect, if any, produced on the infected ani- 

 mals ; (b) the results of various methods of treatment of the 

 infection. 



(3) A study of the life history of the various protozoa, espe- 

 cially Trichomonas. This subject is self-explanatory. Little is 

 known of the life history of Trichomonas. Cysts are not known. 

 Practically nothing is known of the mode of infection with this or- 

 ganism in nature. Much helpful work has been done by Hegner 

 and others along this line. 



(4) Attempts to cause encystation of Trichomonas, using the 

 method o-utlined by Cropper and Drew for free-living anujcbce. 



