[45] _Bull. Soc. Med. Chirurg. Indo-Chine_, v, p. 55.
The parasite under discussion was first observed by Lambl (1859) in the mucous evacuations of children. He regarded the parasite as a Cercomonad and termed it _Cercomonas intestinalis_, which name as a rule is applied to _Cercomonas hominis_, Davaine, although Stein had already pointed out the difference between the two species. Grassi (1879) observed this species first in mice (calling it _Dimorphus muris_), and subsequently in human beings in Upper Italy and named it _Megastoma entericum_. Bütschli and Blanchard then laid stress on the identity of this species with Lambl’s _C. intestinalis_ (1859), and consequently called it _Megastoma intestinale_. Later, Blanchard drew attention to the circumstance that the generic name _Megastoma_ chosen by Grassi had already been used four times for various kinds of animals, and established the genus _Lamblia_. Accordingly, _L. intestinalis_ is the valid name, and should be generally adopted.
In Upper Italy the parasite in the encysted condition has also been seen by Perroncito in man. At the same time, Grassi and Schewiakoff began a new investigation of specimens from mice and rats. In Germany, _L. intestinalis_ was found by Moritz and Hölzl, Roos, Schuberg and Salomon. Moritz and Hölzl confirmed the relative frequency of the species. In Königsberg, Prussia, a student found encysted _Lamblia_ in his fæces. One case was reported from Finland by Sievers, another case from Scandinavia by Müller. Frshezjesski and Ucke reported cases from Russia. Jaksch announced the occurrence of the parasite in Austria; Piccardi mentioned their presence again in Italy. They were reported from Egypt by Kruse and Pasquale, and from North America (Baltimore) by Stiles. Noc stated that 50 per cent. of the population of Tonkin harboured _Lamblia_. Finally, the structure of _L. intestinalis_ has been described by Metzner (1901), and by Wenyon[46] (1907) in mice.
[46] _Arch. f. Protistenkunde_, Suppl. i, p. 169.
In all these cases _L. intestinalis_ has been observed in the small intestine, or in the evacuations of patients with intestinal diseases. It has also been found in the intestine of healthy subjects. Just as _Trichomonas intestinalis_ may be found inhabiting the stomach in diseases of that organ, in which an alkaline reaction is present (carcinoma), so has _L. intestinalis_ been found to occur under similar circumstances (Cohnheim, Zabel). However, in Schmidt’s case, 1 per cent. hydrochloric acid was certainly stated to be present. Infection takes place by the ingestion of cysts (fig. 20, _e_), as was established by Grassi, experimentally on himself. Cereal food-stuffs, contaminated with Lamblia cysts from vermin of the locality, such as rats and mice, serve to convey the infection to man. Such cysts may probably be found in street-dust, etc. Stiles induced infection in guinea-pigs, and Perroncito in mice and rabbits, by means of cysts of Lamblia from human beings. Stiles suspected that flies could transport Lamblia cysts. Mathis (1914) found that _L. intestinalis_ was not amenable to emetine, at any rate in its cystic stage.