THE PRESENT STATE OF KNOWLEDGE OF THE AMOEBAE 9 



to live in the intestine. They measured only 4 /a to 6 fi in diameter, and 

 were almost certainly small degenerating individuals of the flagellate 

 Triclioitionas homiiiis. Although this has been pointed ouc by Leuckart 

 (1863)* and Grassi (1888), modern workersf still continue to cite LambI 

 as the discoverer of the intestinal amoebae of man. 



So far as I have been able to ascertain, the intestinal amoebae of 

 man were really discovered by Lewis (1870) and Cunningham (1871), 

 in the course of their investigations on cholera in India. The amoebae 

 which they studied probably belonged, for the most part, to the species 

 now known as Enlamocba coli — as will be shown later. It is therefore 

 not surprising that these workers concluded that the intestinal amoebae 

 of man are not pathogenic. Soon after the publication of their observa- 

 tions, however, another amoeba was discovered by Losch (1875), in 

 the stools of a patient suffering from dysentery, in Russia : and the 

 discovery of this organism initiated a discussion which subsequently 

 engaged the attention of a large number of workers and lasted for some 

 forty years. The chief point at issue was whether the intestinal amoebae 

 of man do or do not cause dysenter}'. Opposite views were held by 

 different workers and at different periods — the consensus of opinion 

 swinging first to one side and then to the other. 



There appear to me to be two chief reasons why the comparatively 

 simple problems connected with .imoebic dysentery remained so long 

 unsolved. First, there was a failure to realize that the amoebae constitute 

 a large group of organisms, containing many species belonging to many 

 different genera. Of these, man harbours not one but several different 

 kinds ; and all are forms which have nothing to do with the free-living 

 amoebae. The second obstacle in the way to knowledge was the failure 

 to realize that " dysentery " is not one disease, but a symptom of several 

 different pathological conditions. There is no one specific "cause" 

 of all dysenteric symptoms ; and it is now even difficult to conceive 

 how anybody could ever have thought that he had ruled out amoebae, 

 as a cause of dysentery, by simply demonstrating that certain bacteria 

 can also cause it. 



We now know that the amoeba which Losch discovered was 

 Entamoeba histolytica — one of several different species living in the 

 human bowel, and the only one, so far as is known, capable of causing 

 dysentery or any other disease in man. We now know also, however, 

 that this organism does not usually cause dysentery, which is most often 

 the result of infection with certain bacteria. At the time of Losch's 

 discovery bacillary dysentery was not a clearly recognized condition, 

 and all amoebae were regarded — at least by physicians — as suspiciously 

 alike. Losch himself was not convinced that the amoebae which he 

 found were the cause of his patient's illness, and he seems to have 

 regarded them rather as a secondary or accessory factor in the causation 

 of dysentery. Much of the earlier work on the intestinal amoebae was 



* Leuckart (1863, p. 140) drew attention to the similarity of Lambl's figures — 

 which he reproduced — to an organism described from fowls by Eberth. This organism 

 (" Trypanosoma " ebertiti Kent) is now known, since the work of Martin and Robertson, 

 to be a Trichomonas. 



+ Many of them cite a paper published in the Vierteljahrschr. f. prakt. Heilkde., 

 Prag, 1859. In this, however, amoebae are not even mentioned. I fancy few people 

 have really seen Lambl's work of i860, which is very difficult to obtain. 



