GIARDIA INTESTINALIS 123 



The ordinary multiplication of Macrostoina is no doubt similar 

 to that of Trichomonas. When ready to leave the body oval 

 cysts are formed seven or eight n (^^^(j of an inch) in length, 

 within which the animal with its nucleus and large cytostome can 

 be seen (Fig. 32D). Wenyon has found Macrostoma cysts with 

 four nuclei and thinks that some multiplication may occur 

 within the cysts as it does in Endamaeba. The methods of trans- 

 mission and means of prevention differ in no way from those 

 of Trichomonas. 



Giardia (or Lamblia) intestinalis. — Next to Trichomonas, 

 Giardia is the most common flagellate in the human digestive 

 tract. Unlike most of the other intestinal protozoans it estab- 

 lishes itself in the upper part of the small intestine. It is one 

 of the oddest-shaped little animals known. Wenyon aptly 

 describes it as follows: " In shape it resembles a pear split into 

 two parts along the longitudinal axis. There is a fiat surface 

 on which there is a sucking disk with raised edge, and a convex 

 surface. The tapering extremity or tail can be turned over the 

 convex back, and it terminates in two flagella. There are three 

 other pairs of flagella, the arrangements of which are best seen 

 by referring to the plate." (Fig. 33.) 



Giardia is remarkable in being perfectly bilaterally symmetrical, 

 every organelle, including the nucleus, being accurately repro- 

 duced on each side of the middle line. Between the two small 

 nuclei are a pair of rodlike structures (Fig. 33, par. b.) thought by 

 some workers to be parabasal bodies, from which the flagella 

 arise. As seen in face view the parasite has a comical owl-like 

 appearance. This fantastic little animal, 12 to 18 n (^tjV^ to xs'tt 

 of an inch) in length fastens itself to the convex surface of an 

 epithelial cell by means of its sucking disk, resting with its 

 flagella streaming like the barljels of a catfish (Fig. 33F) . Some- 

 times long rows of them can be found resting on the surface of the 

 epithelial cells of digestive glands. Miss Porter, who has studied 

 Giardia infections in British soldiers from Gallipoli, estimated 

 recently that in one case the number of cysts, each having been 

 an active flagellate in the intestine, exceeded 14,000,000,000 in 

 a single stool. The number of cysts in an average stool in a 

 case of moderate infection she estimated at 324,000,000. 



Evidently this flagellate multiplies very rapidly, but its method 

 of multiplication is not fully understood. Division of unen- 



