1922] Kofoid-Swezij: Mitosis and Fission in Giardia rnterka 201 



An added reason for tlie publication of a eritical analysis of the 

 morphological figures of the parasite found in man is the fact that 

 some recently published figures in textbooks and in works specially 

 designed for use in clinical diagnosis or in stool examination (Doflein, 

 1916 ; Cammidge, 1916 ; Hegner and Cort, 1921 ) publish or copy figures 

 of the Oiardia of man which give an incorrect or at least an atypical 

 representation of the parabasal bodies, organs most useful in specific 

 diagnosis in the genus Giardia. Thus Deschiens (1921) in describing 

 the parabasals states that they are " generalement fusionnes et tres 

 polymorphes. " whereas careful focusing with a good binocular micro- 

 scope with immersion monobjective will almost invariably resolve the 

 pair of parabasals accurately. 



ilATERIAL AND METHODS 



Our material is all from human faeces and presumably belongs to 

 a single widely distributed species parasitic only in man. It has 

 included large and small races and infections in which ellipsoidal as 

 well as spheroidal, or even elongated cysts were present. In the 

 absence of other structural distinctions than those of size and propor- 

 tions of the cyst, we incline to the view that these relatively rare but 

 divergent forms are at the most but mere races within the variable 

 species. It is quite within the range of possibilities that the species 

 parasitic in the rodents may at times establish a foothold in man, but 

 experimental tests of their capacity to do this and of the degree of 

 host specificity prevalent in the genus Giardia are as yet lacking, 

 except in the case of the experimental transfer of the human Giardia 

 to kittens by Fantham and Porter (1916) and by Deschiens (1921). 



Our material came in part from stool examinations made on 576 

 home service (37 cases, 6.4 per cent) and 2300 overseas soldiers (131 

 cases, 5.7 per cent) at the Army Laboratory, Port of Embarkation, 

 New York City, in 1918-1919 (see Kofoid, Kornhauser, and Plate, 

 1919, and Kofoid, 1919), and in part from over 9000 routine stool 

 examinations made in the Parasitological Laboratory of the California 

 State Board of Health of residents of California, including persons 

 from other states of the Union and from Mexico, Central America, 

 the Hawaiian and the Philippine Islands, China, Japan, Persia, India, 

 Siberia, and Armenia. It is thus presumabl.y widely representative of 

 exposures to human infections, though we have no means of establish- 

 ing the actual geographical sources of the infections we have studied. 



