Like Trichomonas, Lamblia can multiply under inflammatory conditions of the alimentary tract. Thus they are found in cases of diarrhœa, carcinoma of the stomach, etc. The parasites attach themselves by their sucking discs to the epithelial cells of the gut (fig. 20, _c_), and though their numbers may be very great, their direct pathological significance is not fully known. Their occurrence in cases of diarrhœa has been explained as being due to the increased peristalsis, which has detached the parasites from the epithelium. Free flagellate forms perish in stools if kept, more especially if the temperature falls below 0° C. or rises above 40° C. Lamblia has often been found in dysenteric diseases, especially in the East, and is said to be the causal agent of certain diarrhœas in India. Mathis (1914)[45] found Lamblia in cases of diarrhœa with dysenteriform stools in Tonkin. He also discovered healthy carriers of Lamblia cysts. [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.