134 PROTOZOAN PARASITISM 



ganisms immediately when considerable numbers are 

 present. Prolonged examination of several prepara- 

 tions will usually reveal sparse infection. When 

 picked up by low magnification they may be then 

 studied under higher power objectives. 



Mixing a portion of the specimen wdth 0.9% sodium 

 chloride solution and placing in the incubator for a 

 short time, until well warmed, will activate organisms 

 which have become sluggish and will reveal parasites 

 otherwise overlooked. 



It is seldom that the trophozoite of a flagellate 

 does not appear in a liquid stool examined properly 

 immediately after passage or after being kept warm 

 for a short time, when it is present in the intestine. 

 For that reason the cysts are relatively unimportant 

 from the standpoint of such an examination. They 

 are more important in survey work, when large num- 

 bers of specimens are to be examined, or when ex- 

 amination cannot be done immediately. Such ex- 

 aminations are likely to miss Trichomonas and other 

 flagellates when they are present only in the active 

 stage. 



The active forms of the flagellates are readily 

 identifiable and there is little or no excuse for con- 

 fusion of them, except some of the more minute un- 

 common species. Even in the most actively motile 

 state, one learns to recognize Trichomoiias, Chilo- 

 mastix and Giardia by their manner of movement. 

 Giardia has an easily recognized shape. Seen antero- 

 posteriorly it is of pear shape with broad anterior 



