HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



such as exist in the case of Giardia, Chilomastix, etc., 

 and the trophozoites round up and become quiescent soon 

 after leaving the bodies and in this condition it is almost 

 impossible to find them. 



Fresh material and culture methods. When fresh fecal 

 material is examined by the smear method or when com- 

 paratively fresh feces are cultured the percentage of 

 positive cases increases at once. Hegner and Becker 

 (1922) found that the smear method revealed only one 

 infection with T. hominis in no specimens from differ- 

 ent persons; but four were discovered by the culture 

 method. Similar results were obtained by Reichenow 

 (1923). The examination of fresh fecal specimens by the 

 smear method in tropical America (Hegner, 1925a) 

 gave an incidence of infection with trichomonads of 20.6 

 per cent. This result was probably due in part to a high 

 rate of infection among the persons examined but the 

 fact that the stools were fresh was an important factor. 

 Recently Hill (1926) reported a more extensive compari- 

 son of the smear and culture methods in Porto Rico 

 under field conditions. Of 912 persons examined, the 

 smear method revealed 16 infections with trichomonads 

 and the culture method 84 and all of the 16 specimens 

 found positive when smears were examined were also 

 found positive when cultures were made. Hill also found 

 that smears from fresh stools gave a higher incidence 

 than those from older stools; thus, smears from feces 

 that were 6 to 20 hours old gave 3 positive cases, or 0.5 

 per cent, from 612 persons; whereas smears from feces 

 that were 2 to 6 hours old gave 13 positive cases, or 4.3 

 per cent, from 300 persons. The latter were all children 



144 



