jS THE AMOEBAE LIVING IN MAN 



Wenyon (1908), Brutnpt (1909), and others, should not be overlooked. 

 Rodents — e.g., mice — also harbour Entainoebae which are not at present 

 distinguishable with certainty by any character, save their habitat, from 

 Entamoeba coli. Brumpt (1910), indeed, formerly included the amoebae 

 from mice, rats, guinea-pigs, and monkeys under E. coli — or, as he 

 wrongly called it, ''Amoeba coli Losch." At present, however, this 

 comprehensive conception of the species seems premature. 



Description. 



Entamoeba coli is one of the largest of the amoebae of man, though 

 subject to great variation in size. Rounded individuals, belonging to the 

 ordinary active stage of the organism, may have any diameter from about 

 18 yu, to 40 /i. As a rule, however, in my experience, their diameter lies 

 between 20 /a and 30 fx. As regards size, therefore, this species closely 

 resembles E. histolytica. The living organisms, examined immediately 

 after leaving the human body, are typically distinguishable from the 

 latter species by the following characters : 



They are far less active, as a rule merely showing changes of shape 

 unaccompanied by active locomotion. Sluggish movements are charac- 

 teristic of this species ;* and the sudden extrusion of clear, blade-like 

 pseudopodia — so often seen in E. histolytica — is never observable. Their 

 ectoplasm is also far less differentiated, and the line of demarcation 

 between it and the endoplasm usually not conspicuous. Their endo- 

 plasm is very bulky and granular, and usually heavily charged w^ith food 

 vacuoles containing various inclusions, but not red blood corpuscles or 

 tissue elements. The nucleus is usually very conspicuous, appearing as 

 a round or oval beaded ring, lying as a rule in an eccentric position. 

 There is, of course, no contractile vacuole ; but E. coli often contains 

 vacuoles of a peculiar form,t resembling clefts or dilated cracks with 

 pointed ends, and containing a liquid — possibly water. These vacuoles 

 are quite different in appearance from the bubble-like vacuoles so com- 

 monly seen in degenerate E. histolytica. Whether, like these, they are 

 formed as a result of degeneration I have not determined. 



The food vacuoles may contain all manner of food derived from the 

 contents of the bowel, and they give this species a very characteristic 

 appearance in life. The structure of the cytoplasm is difficult to make 

 out in consequence, but as a rule it appears coarser and more granular 

 than that of E. histolytica. It often appears somewhat greenish in 

 colour — probably owing to the contained granules. The colour, though 

 slight, is quite distinct when individuals of the two species are seen 

 lying side by side — E. histolytica appearing whitish and E. coli greenish. J^ 



* Wenyon and O'Connor (191 7) state that E. coli may sometimes show movements 

 quite as active as those of E. histolytica. Though I do not question their observation, 

 I may say that I have never been fortunate enough to see such lively specimens, and 

 they must be very rare. 



t These are shown in the amoeba depicted in fig. 55, PI. IV. 



X This description refers to the appearance of the amoebae under an ordinary 

 achromatic lens. Under an apochroniat, with good illumination, there is no appre- 

 ciable difference in colour. The difference usually seen depends, therefore, in all 

 probability, upon the difference in the granulation of their cytoplasms. It is purely an 

 optical effect, and not due to the presence of any colouring matter. 



