INTRODUCTION xvii 



with the presence of protozoa and among physicians 

 in estimating the significance of the finding of pro- 

 tozoa in a sick person. 



Particularly is the practicing physician prone to 

 err when he is searching for the cause of a confusing 

 disease and finds such an optically prominent thing 

 as a protozoon in the stool. It appears as if it should 

 be doing something harmful. The physician does 

 not ordinarily become so concerned about the myri- 

 ads of bacteria also present. They are not so promi- 

 nent to the eye. This prominence of the relatively 

 large protozoa is undoubtedly responsible for the 

 difficulty which many have in passing them by. One 

 may well wonder if more actual harm than good has 

 not come from routine stool examination, as used 

 up to the present time. 



