OF THE ALIMENTARY TRACT 179 



hosts. As pointed out by Dobell ( 1920) it was prob- 

 ably first seen by Leeuwenhoek, the father of Proto- 

 zoology (1681), who found himself to be a host of it. 



Lambl in 1859 and 1860, Grassi (1879), and Blan- 

 chard (1888) are the early students concerned with 

 its history. 



Until the past few years it was thought to be an 

 uncommon parasite and there was little study of it 

 except an occasional report of its presence in some 

 person, usually a child, who had diarrhoea. 



Of late, it has come into more general recognition 

 as a very common intestinal flagellate, especially in 

 children. 



Kofoid, Kornhauser and Plate (1919), in one of the 

 earliest studies of a large number of persons, found 

 1500 United States soldiers, 300 of whom had not 

 seen foreign service, to harbor it in 6% . Hegner and 

 Payne (1921) arrived at an average incidence in 

 20,000 reported cases of 12%. Boeck and Stiles 

 (1923) give an incidence of 6.5% in 8029 persons, 

 many of whom were children, examined by them. 

 Thomas and Baumgartner (1925) found only 2.5%o 

 incidence in female institutional inmates. Maxcy 

 (1921) found about 20% of 74 children between one 

 and thirteen years of age infested. In England, Mat- 

 thews and Smith (1921) found 14% of 548 children, 

 Campbell (1921) found 16% of children under twelve 

 years, and Nutt (1921) found 48.8% of institutional 

 children and 23.9% of hospitalized children, to har- 

 bor the parasite. 



