194 FAMILY: AMCEBIDiE 



(1924 a) state, however, that they have examined the material from this 

 case, and can confirm the occurrence of E. histolytica in the skin lesions. 

 Furthermore, they claim to have seen another case showing the same 

 infection. 



Smith, S. (1924) states that he has seen amoebse in pus from a knee- 

 joint, while Sharp and Morrison (1925) claim to have found them in pus 

 from abscesses in muscles. 



MORPHOLOGY. — The morphology of E. histohjtica may be considered 

 under three headings corresponding with the three phases of. development 

 — namely, the tissue-invading form, the precystic form, and the cyst. 



1. Tissue-Invading Forms. — These may be regarded as representing 

 the most active phase of development (Plate I., p. 192). They occur 

 normally in the walls of the intestinal ulcers and of the secondary lesions 

 produced in other parts of the body. They are to be found in the faeces 

 after discharge from the ulcers, in the pus draining from abscesses of the 

 liver and other organs, or in material coughed up after rupture of an 

 abscess into the lung. As has been pointed out by Dobell (1919), the 

 amoebae begin to degenerate soon after they have left the intestine, an 

 explanation of the many discrepancies which characterize the accounts 

 of the morphology of E. histolytica and the attempts at the establishment 

 of new species. Even when the amoebae are seen in perfectly fresh stools 

 within a few minutes of their escape from the body, changes may already 

 have occurred during their passage down the large intestine. It thus 

 happens that in most cases in actual medical practice a diagnosis has 

 to be made from forms which are abnormal, and which do not show the 

 true structure of the nucleus and cytoplasm of the amoebae as they appear 

 in the living tissues. Such alterations in character, however, do not 

 necessarily lead to the death of the amoebae, for kittens may be infected 

 by injection of material which was passed many hours before. 



The tissue-invading form of E. histolytica as a rule varies in diameter 

 from 20 to 30 microns, but larger or smaller forms may occur (Fig. 95, 1-4). 

 A very characteristic feature of the amoeba is its activity, large, 

 blunt pseudopodia being formed and withdrawn in rapid succession. 

 Progression in one direction is effected by the formation of a pseudopodium 

 and the flowing of the entire cytoplasmic body into it. The pseudopodia 

 are often formed quite suddenly with almost explosive violence. The 

 remarkable activity of a group of these amoebae when seen in a freshly 

 passed and still warm portion of mucus can only be appreciated when 

 seen; no description can give a satisfactory picture of this really extra- 

 ordinary phenomenon. Not infrequently the amoebae become elongated 

 and glide in a slug-like manner over the surface of the slide without 

 noticeable change in shape. In so doing the posterior end may have 



