HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



toms ; they are carriers. A few individuals, however, are 

 afflicted with a diarrheic condition that is very persist- 

 ent; the presence of large numbers of giardias in their 

 stools and the absence of any other organisms that are 

 known to be the etiological agents of diarrhea indicate 

 but do not prove that the giardias are responsible. Diar- 

 rhea is known to result from the irritation of the epithe- 

 lial cells of the intestinal wall (see p. 96) and no doubt 

 such irritation is brought about when vast numbers of 

 giardias are moving about in the duodenum and attaching 

 themselves by means of their sucking discs to the surface 

 of the cells. When few in number the symptoms produced 

 in this mechanical way would be so slight as to pass 

 unnoticed but millions of specimens present at one time 

 might aggravate conditions and bring about diarrhea. 

 Giardias in large numbers might also be injurious to the 

 host as a result of the excretion of waste products or 

 possibly some specific toxic substance, and might even 

 hinder digestion and absorption because of interference 

 with the glands and epithelial cells as Haughwout ( 1918) 

 has suggested. 



Cholecystitis. What appear to be secondary sites of 

 infection for Giardia lamblia are the bile ducts and gall 

 bladder. Many reports have appeared in the literature 

 during recent years of infections in these organs, but 

 these reports are confusing and it is difficult at present 

 to arrive at definite conclusions. Boyd (1921) and Silver- 

 man (1923) reported cases in which the microscopic 

 examination of the liquid obtained by duodenal tubage 

 revealed numerous trophozoites of giardia ; this was soon 

 followed by a description of three similar cases by Libert 

 160 



