150 RESEARCH IN PROTOZOOLOGY 



tolytica since this species was successfully cultivated by Boeck and 

 Drbohlav (1925). 



/. Specific differences based on morphology. The genus Giardia 

 is of peculiar interest because in almost every case each host 

 species contains a distinct species of Giardia that can be distin- 

 guished morphologically from other species. In Fig. 14 are pre- 

 sented diagrams of seven species that show measurements and 

 morphological characteristics of importance in diagnosis. The 

 criteria used in separating these species are first those relating to 

 size. Investigators who have made studies of size in protozoa know 

 that size is a very constant characteristic. The measurements of im- 

 portance are total length, not including the caudal flagella, breadth 

 across the ventral sucker, ratio of length to breadth, the distance 

 from the anterior end to the center of the nucleus, from the center 

 of the nucleus to the end of the lateral shields, the distance from 

 the end of the lateral shields to the posterior end of the body, and 

 the distance across the body at the ends of the lateral shields. The 

 contour of the body is of importance. In Giardia lauiblia from man 

 (Fig. 14, a), for example, the lateral shields taper gradually to 

 their posterior ends, whereas in Giardia duodcnalis, from the rab- 

 bit (b), and Giardia cavice, from the guinea-pig (g), the lateral 

 shields bulge outward. The distance of the nuclei from the median 

 line and from the posterior edge of the sucking disc and their posi- 

 tion in the body, whether parallel to the axostyle or obliquely situ- 

 ated, are of importance. The size and shape of the nuclei are also 

 diagnostic characteristics of value. In giardias fixed in Schaudinn's 

 solution and stained with iron hematoxylin the parabasal bodies 

 are usually conspicuous. These bodies are very constant in num- 

 ber, shape and position. For example, Giardia agilis from the frog 

 tadpoles has a single club-shaped parabasal body lying parallel to 

 the axostyle. The Giardia from the rabbit (Fig. 14, b) has two 

 long, slender parabasal bodies slightly bent near the center and 

 lying obliquely across the axostyles and G. muris from rats and 

 mice (Fig. 14, c) possesses two oval parabasal bodies that lie side 

 by side and parallel to the axostyle. Another characteristic that 

 may be of diagnostic value is the affinity for iron hematoxylin 

 stain. The writer (Hegner, 1925), for example, found it very 

 difficult to stain the giardias from birds by methods that produced 

 beautiful preparations of specimens from other hosts. By means 

 of the criteria set forth it seems possible to distinguish various 



