12 THE AMOEBAE LIVING IN MAN 



little etfect. Upon medicine, however, Musgrave and Clegg's work has 

 still left its impression ; and from time to time others still fall into the 

 same errors. The chief merits of their work consisted in their improve- 

 ments in the methods of cultivating free-living amoebae, and their 

 introduction of the now current term " amoebiasis," to denote a state of 

 " infection with amebas." 



The publications of the first decade of the present century make, 

 for the most part, unpleasant reading. The German workers — Prowazek, 

 Hartmann, and others — continued along the path of error indicated 

 by Schaudinn. Craig, in America, and many others, followed in their 

 train, and their "confirmations" of Schaudinn's work, coupled with the 

 discovery at intervals of new "species" of amoebae in man, served 

 only to make matters worse. A present-day seeker after the truth, 

 completely ignorant of the subject, would obtain more reliable infor- 

 mation by consulting the works published prior to 1900 than those 

 which appeared during the next ten years. In the latter period almost 

 the only observation of any real value was made by Huber (1903), but 

 it was stifled by the authority of Schaudinn and the other German 

 workers. Huber rediscovered and first investigated the cysts of the 

 dysentery amoeba — formerly found by Quincke and Roos — and really 

 supplied the chief deficiency in our knowledge of this organism. The 

 rediscovery of these cysts by Viereck (1907), Hartmann (1908), and 

 Elmassian (1909), — who all described them as belonging to new species 

 — did not mend matters. No real advance was effected until the com- 

 pletion of the epoch-making work of E. L. Walker in the Philippine 

 Islands. This work must now be considered. 



Walker made an unpromising beginning. His hrst paper (1908) 

 repeated many of the errors of his predecessors. He was unable to 

 distinguish the free-living from the parasitic species of amoebae, and 

 confused forms which he was able to cultivate, with those found in the 

 intestinal contents of man and other animals. A second paper, pub- 

 lished three years later, marked an immense stride forward. Walker 

 (191 1) was then able to draw the following conclusions* from his 

 researches : 



(i) The amoebae found in the Manila water supply, and those 

 cultivable from the intestinal tract of man, all belong to the genus 

 Amoeba Ehrenberg. These species are not parasitic in the intestine 

 of man. When amoebae are obtained in cultures from the intestinal 

 contents, they are derived from ingested cysts which have passed 

 unchanged through the intestine. 



{2) The amoebae parasitic in the intestinal tract of man belong to 

 a distinct genus, Entanioeha Casagrandi and Barbagallo. They are 

 obligatory parasites, and cannot be cultivated. Two species are recog- 

 nizable — one non-pathogenic [Entamoeba coli) and one pathogenic 

 {E. histolytica). The first forms cysts containing 8 nuclei ; the second 

 cysts containing 4 nuclei. The organisms are transmitted from man 

 to man by means of these cysts. 



In his final paper, published in collaboration with Sellards (1913), 

 Walker was able to supply proofs of all these statements, as a result of 



* I have modified and condensed these conclusions somewhat, so that they are not 

 given here in Walker's own words exactly. 



