RELATIVE FREQUENCY 715 



The species of Giardia, ChUomastix, and T richomonas are more exten- 

 sively known, and can be considered to be world-wide in their distribution. 

 As the two former can be recognized by their cysts, they can be detected 

 in the formed as well as the diarrhoeic stool, whereas the latter is only 

 rarely seen in the formed stool owing to the absence of the encysted forms. 



G. intestinalis was found by the writer and O'Connor (1917) to be 

 present in 4-1 to 



16 per cent, of ..^rSt. . rx B 



normal individ- 

 uals in Egyj)t. 

 Dobell (1921) 

 estimates that 

 18 to 27 per cent, 

 of the artisan 

 population of 

 the British Isles 

 harbour this 

 flagellate, while 

 Boeck (1921) 

 found it present 

 in 48-1 per 

 cent, of eighty- 

 three industrial 

 school children 

 examined in 

 America. 



As regards 

 C. mesnili, the 

 writer and 

 0'Connor(1917) 

 obtained a per- 

 centage of 3-2 

 of infections 

 amongst nor- 

 mal individuals 

 in Egypt. For 



the population of the British Isles, Dobell gives 6 to 9 per cent., while 

 Boeck gives 1-2 for American school children. 



T. hominis was seen by the writer and O'Connor in only 3 per cent, of 

 hospital cases in Egypt, and in a much smaller percentage of healthy 

 people. Amongst the population of Britain, Dobell mentions that it was 

 only occasionally seen, while it was not met with at all by Boeck m his 

 examinations of American school children. 



Fig. 303. — The Flagellates of the Human Intestine 

 (x 2,000). (After Wenyon, 1922.) 



A-C. Giardia intestinalis, free and encysted forms. 

 D-F. ''Iii/oiini^ti.r iiir.^)/l/i. free and encysted forms. 



G-I. I'lniiiiiilniiiniiit-i i iilr^il iKiIis. free and encysted forms. 



J-L. Tnci n-diuuiris iiitisiiii(i/is. free and encysted forms. 

 M-0. Trichomonas hominis, forms with three, four, and five flacrella. 



