34 THE AMOEBAE LIVING IN MAN 



these descriptions are all based upon defective and insufficient material 

 anybody can easily convince himself, if he will take the trouble to obtain 

 really fresh and healthy amoebae, and study them with sufficient care 

 and with proper cytological technique. All the abnormal forms of 

 nuclei so often described as normal can be made at will by simply 

 keeping normal individuals until they degenerate and die. 



Hartmann (1908, et alibi) lays great stress upon the occurrence of 

 "cyclical changes around the karyosome " in £. histolytica. In normal 

 individuals, however, these are never seen. His "cycle" represents 

 an arbitrary series of degenerate forms with various arrangements of 

 chromatin between the karyosome and the nuclear membrane. All these 

 forms are common in stale stools or liver-abscess pus. But they are not 

 encountered in really fresh and well-fixed material, in which the nuclear 

 structure is constantly as I have just described it. 



The differences so often described between the nuclear structure of 

 E. histolytica and " E. tetragena" are clearly due to misunderstandings of 

 various sorts, since these names are synonymous. I do not understand 

 the views of those who still — whilst admitting the synonymy — distinguish 

 between "histolytica" and "tetragena" forms of this amoeba. The 

 distinction is, in any case, quite unjustifiable. 



General Outline of the Life-history. — The life-history of E. histolytica in 

 man is very simple. The active amoebae just described live in the tissues 

 of the gut wall, where they multiply by division. In a typical " normal" 

 infection, a certain proportion of the amoebae constantly leave the ulcers 

 and pass into the lumen of the large bowel, where they encyst and later 

 pass out, in the encysted form, with the faeces. The precystic amoebae, 

 which are thus free in the lumen of the bowel, are smaller than the ordinary 

 forms which continue to multiply in its tissues. They are entirely free 

 from cytoplasmic inclusions, and are in all probability formed simply by 

 division of the larger tissue-inhabiting individuals. The cysts, which are 

 found only in the faeces, are slightly smaller than the precystic amoebae, 

 and when fully developed are quadrinucleate. They vary greatly in size ; 

 and it has been shown that there are at least several distinct races of the 

 parasite distinguishable by the size of the cysts which they form. When 

 the cysts are swallowed by a human being, they probably hatch in the 

 small intestine and liberate small amoebae, which pass down with the 

 intestinal contents into the large bowel. Here they attack and invade the 

 tissues, and thus begin the cycle of development anew. No other stages 

 are known to occur normally in the life-history. In exceptional circum- 

 stances, however, a complication in development may result from the 

 migration of the amoebae from their primary site of infection into the 

 liver, brain, or other organs. If they succeed in establishing themselves in 

 these secondary sites they cause abscesses, which may give rise to further 

 pathological complications. The amoebae in secondary infections of the 

 organs are always of the typical tissue-inhabiting form — precystic 

 amoebae and cysts being found in the intestinal contents only. Such 

 secondary infections are clearly accidents in the life-history of the 

 amoeba. They do not form a part of its normal cycle of development, 

 but must be regarded as side-issues resulting from the straying of certain 

 individuals from their normal or primary habitat, which is undoubtedly 

 the wall of the large intestine. However important such migrations 

 may be for man from a medical point of view, they are of no use to the 



