ANIMAL PARASITES 69 



Unfortunately, the Giardia cysts break down in this fluid after a few 

 months. 



Permanent slides of any of the species to be used in this exercise 

 should be made by fixing moist smears in hot Schaudinn's fluid and 

 staining in iron hamiatoxylin (see p. 99). When possible, smears 

 should be made from a fragment of the infected intestinal wall as 

 well as from the intestinal content. Special care should be observed 

 in differentiating the stain. 



CHARACTERISTICS OF INTESTINAL MASTIGOPHORA 



Of the many forms of intestinal flagellates we shall give special 

 attention to three genera — Chilomastix, Trichomonas, and Giardia 

 — not only as widely distributed forms, but also as genera repre- 

 sented by parasites of man. The consideration of them together 

 is only a matter of convenience for, from a systematic viewpoint 

 they represent distinct families. One of them, Giardia, is a 

 member of a special order of Mastigophora, the Diplomonadida, 

 or "double monads," characterized by a bilateral symmetry of 

 the body, with two nuclei, eight flagella, and all of the organelles 

 paired. The distinguishing characteristics of this and of the 

 Chilomastigidse and Trichomonadidae will be brought out in the 

 laboratory work. 



PRACTICAL WORK 



Examine, when possible, both living and stained specimens 

 of the following representative parasites or related species from 

 animals. Note the size, movements, structures, features, and the 

 characteristics of the cysts when present. 



Chilomastix mesnili is a fairly common parasite of the small 

 intestine of man which has often been confused with Trichomonas 

 intestinalis. It is pear-shaped with a rounded anterior end and 

 a pointed posterior end. It has a characteristic jerky, spiral 

 movement. The size varies greatly, the average being about 

 14ju in length by 6/x in breadth. The relatively large, round 

 nucleus is at the very anterior end, dorsal to the cytostome 

 ("mouth"). The three anteriorly projecting flagella should 

 be examined in favorable specimens, with careful adjustment 

 of the iris diaphragm of the microscope. In properly stained 

 specimens under high magnification it may be seen that they 

 arise from minute, dotlike blepheroplasts. A fourth flagellum 

 lies within the large elongate cytostome and probably functions 



