OF THE ALIAIENTARY TRACT 127 



The problem of the effects of these parasites upon 

 man has reached a stage of impasse. None of the 

 class has been shown to be an actual tissue invader 

 or destroyer, none has been shown to produce any 

 substance or bring about any state deleterious to the 

 host. There is no positive direct evidence on the 

 question, it is all clinical circumstantial evidence 

 based upon the occurrence of indefinite symptoms of 

 abnormal states associated with the presence of the 

 parasites. Such evidence, if it were definite and 

 characteristic, would weigh more than it does. There 

 is no typical or characteristic clinical complex to 

 be related to the presence of any of them. 



Until better identification of the organisms and 

 more careful relation of them to definite clinical 

 states is done in medical practice the question will 

 remain as it is, unless experimentation develops more 

 bearing than it has. 



It was thought that cultivation, Avhich may now be 

 done with all except Giardia, would initiate some di- 

 rect avenue of approach, perhaps through isolation of 

 the organisms and experimental infection. Thus far 

 this has not occurred, cultures have not been devel- 

 oped which are usable in such work. Neither is 

 animal experimentation satisfactory. It is most 

 difficult to judge or control the absence of like para- 

 sites in experimental animals. 



The species of flagellates found in the alimentary 

 tract of man are apparently specific for him. We 

 probably do not obtain these organisms from other 



