III. 



THE PRESENT STATE OF KNOWLEDGE OF THE 

 AMOEBAE LIVING IN MAN. 



Before I attempt to give detailed descriptions of the amoebae which 

 live in man, I will devote a short space to a general account of our 

 knowledge of the whole subject ; my object being to indicate, by means 

 of a brief historic survey, the present state of knowledge concerning all 

 the amoebae which live in human beings, and the more important of the 

 steps by which this knowledge has been acquired. 



By far the greater part of the literature on this subject deals with the 

 amoebae which live in the intestine. These have always been of par- 

 ticular interest to the physician, on account of their relation — real or 

 supposed — to dysentery and other pathological conditions. But it is 

 only within the last half-dozen years that the medical problems con- 

 nected with these organisms have been fully elucidated : and it is 

 probable that many more years will yet elapse before the knowledge 

 which we now possess becomes generally current in zoology and 

 medicine. It is a familiar observation that it is often more difficult to 

 establish a truth than to perpetuate an error : and of this the history of 

 the present subject already supplies abundant illustrative instances. 



Amoebae appear to have been first found in man by Gros (1849) in 

 Russia, who discovered and briefly described the amoeba now known as 

 Entamoeba gingivalis, which lives in the mouth, Steinberg (1862), 

 Grassi (1879^), Kartulis (1893), and Prowazek (1904), all rediscovered the 

 same organism later, and in recent years it has acquired some notoriety. 

 The earlier workers appear to have regarded it as a harmless organism : 

 but Bass and Johns (1914, 1915), Smith and Barrett (1915), and other 

 more recent investigators — especially in America — have upheld the 

 hypothesis that it is the cause of pyorrhoea alveolaris, and consequently 

 a pathogenic parasite of considerable medical importance. Much work 

 has since been done on this subject, and it now appears more than 

 probable that the earlier workers — as is so often the case — had the 

 clearer vision. At the present moment all the evidence points to the 

 conclusion that E. gingivalis is an inoffensive commensal, which man 

 very commonly, but unsuspectingly, lodges in his mouth. It seems 

 unlikely that the future will reveal any further facts of fundamental 

 importance concerning this amoeba. 



It is generally said that the intestinal amoebae of man were dis- 

 covered by Lambl, in Prague. This is, I think, an error. It is true 

 that Lambl (i86o) reported the finding of "amoebae" in the intestine 

 of a child dead of enteritis ; but as he also found " Diiflugia " and 

 " Arcella " in the intestinal contents, his observations are open to grave 

 suspicion — as Leuckart (1863) long ago pointed out. His "amoebae," 

 moreover, can hardly have belonged to any of the species now known 



