GIARDIA INTESTINALIS 



467 



genera Mus and Epimys (M. musculus, E. rattus, E. norvegiciis, 

 M. silvestris) ; also in species of Arvicola {A. arvensis and A. amphi- 

 bius); also in the rabbit, the cat, the dog, the sheep, and man. 



It was first observed by Lambl in the mucous intestinal evacuations 

 of children in Russia ; tlien by Grassi in Itaty, who made a complete 

 study of the parasite; by Moritz in Germany; by Jaksch in Austria; 

 by Kruse in Egypt ; and we have observed it several times in Ceylon; 

 while it has been carefully studied by Werner in 1901, and more 

 especially by Wenyon in 1907 and 1916, and his account is classical. 

 It is common in the Anglo-Egyptian Sudan. 



It occurs in the small bowel of man, and it and its cysts can be 

 found in the faeces. Infection is brought about by swallowing the 

 encysted forms. This has been proved experimentally by Grassi, 

 and as it occurs in mice, it is quite easy to see how infection of 

 foodstufts is passible. 



G. intestinalis is an actively motile organism 

 about 12 to 21 iJi in length, and about 5 to 12 

 in breadth . It is pear-shaped, being surrounded 

 by a thin periplast (ectoplasm), which keeps 

 its form. The under surface (when attached) 

 is excavated with a well-defined border, which 

 is interrupted at the site of the cytostome. 

 This hollow is probably a kind of peristome, 

 and is useful in fixing the parasite to the 

 intestinal epithelium. 



There are two oval nuclei, with ' definite 

 nuclear membranes and with large irregular 

 karyosomes in their centres. There is no 

 connection between these nuclei, but between 

 them lie two darkly staining rods with ex- 

 panded ends, and which posteriorly are con- 

 tinuous with the prolongations of the posterior 

 flagella into the body. From the thickened 

 posterior ends of the two rods spring the mesial pair of flagella, 

 while at their anterior ends is a small granule, from which arises 

 the anterior pair of flagella, which, running forwards and inwards, 

 cross one another and pass across the peristome, or sucking disc 

 or sucker, to its raised margin, around which they run, forming a 

 kind of membrane, till nearly at the level of the nucleus they 

 become free on each side. 



From the same anterior pair of granules there arise the second 

 and finer pair of mesial flagella, running down on the mesial aspect 

 of the nuclei, behind which they turn outwards along the margin of 

 the sucker and finally become free. 



Sometimes there is a row of granules extending from the anterior 

 granules to the ^nucleus on the same side. 



Behind the two nuclei there is a triangular area, which forms a 

 groove running towards the tail . Dorsal to this groove lie two darkly 

 staining masses. 



Fig. 145. — Giardia 

 intestinalis (Lambl, 

 1859). 

 (After Wenyon.) 



