THE CULTIVATION OF INTESTINAL PROTOZOA 67 



The cultivation of an organism, even though by a method which 

 has previously been found a successful one, is often attended by 

 numerous failures. Some of the common reasons for failure 

 are: 



(a) The presence of bacteria, in the material used, which form 

 products harmful to the growth of the protozoa present. The great 

 variety of intestinal bacteria, and the constant change from day to 

 day in the intestinal flora easily explains why an attempted culture 

 of intestinal protozoa may be successful at one time, and not at 

 another. 



(b) Another common cause for failure is the presence of other 

 protozoa which may grow more rapidly than the organism under 

 attempted cultivation. The yeast-like organism, Blastocystis, has 

 been found in the hands of the writer to be one of the most 

 troublesome contaminants. 



(c) A third reason for failure is the use of material which has 

 been kept for too long a time after removal from its original 

 habitat. 



SUGGESTED METHODS OF APPROACHING PROBLEMS OF CULTIVATION 

 OF ANY ORGANISM 



In approaching a problem of cultivation, it is essential that pro- 

 visions be made for the following: 



1. A plentiful supply of the organism to be cultivated. 



2. A means of preserving the organism in as fresh state as 



possible while attempting its cultivation, keeping it free 

 from exposure to the air and refraining from mixing it 

 with unsuitable media. 



3. The determination of the proper concentration of the simple 



medium used as the base for a culture fluid. 



4. The determination of the proper range of hydrogen-ion con- 



centration in the basic medium. 



5. The determination of the proper substance, or substances, 



for the nourishment of the organism. 



6. The determination of the proper oxygen requirements of 



the organism. This is best controlled by the height of the 

 column in the tube of medium used. 



7. The determination of the proper oxygen tension. This is best 



controlled by heating the upper portion of the tube at 



