GIAEDIA INTESTINALIS 703 



various structures are more readily detected (Plate II., 23, p. 250). Within 

 the cyst the flagellate ultimately divides into two, but the process of 

 division is an exceedingly complicated one on account of the numerous 

 structures present. The cysts, like those of other intestinal Protozoa, 

 vary in their permeability to stains and other reagents. On this account, 

 good pictures of the cyst content are only obtained in the case of permeable 

 cysts. As pointed out above, G. intestinalis is sometimes seen dividing 

 in the free condition. As the flagellate possesses no cytostome and the 

 cytoplasm is free from food vacuoles, it is evident that nourishment is 

 effected by the absorption of fluid nutriment through the surface of its 

 body. Bacteria are sometimes seen in evidently degenerate forms. 



Pathogenicity. — The question of the pathogenicity of G. intestinalis, 

 as that of other intestinal flagellates of man, has given rise to considerable 

 controversv. It is an undoubted fact that the flagellates are rarely seen, 

 except in diarrhoeic conditions, but that they are often present in normal 

 individuals can be demonstrated by the finding of cysts in the formed stool. 

 The number of cysts present in the stools are subject to fluctuations. They 

 may be absent from the stool for varying periods, and reappear again later. 

 Certain individuals are known to have remained infected for many years 

 without showing any symptoms, but this fact cannot be raised as an 

 argument against the occasional pathogenicity of the flagellate, as the 

 same condition frequently occurs in infections with Entxmioeha histolytica. 

 In some cases of Giardia infection there occur periodic attacks of diarrhoea 

 associated with the passage of large quantities of clear mucus, in which 

 enormous numbers of free flagellates occur. It is difficult to avoid the 

 impression that this mucus has been produced at that part of the intestine 

 where the flagellates are most numerous, and is the result of irritation set 

 up by their presence. It is possible that in certain individuals which are 

 more susceptible than others, the attacks of diarrhoea correspond with 

 periods of active multiplication of the flagellate. 



In the case of animals, as, for instance, the rabbit, which is commonly 

 infected with a species of Giardia, sections of the small intestine may show 

 all the glands packed with organisms either free in the lumen of the duct 

 or applied to the surface of the cells. When such a condition exists in 

 man, it would not be surprising if the gland cells were irritated by the 

 presence of such large numbers of flagellates. There does not appear to 

 be any tendency for the flagellates to cause ulceration or to penetrate the 

 epithelial surface. The majority of observers believe that G. intestinalis 

 may give rise to intestinal disorders, but the absolute proof of this is 

 difiicult to obtain. The diarrhoeic condition associated with an infection 

 is often spoken of as dysentery, but actually true dysentery does not 

 result. Though quantities of mucus may be present and the stools 



