44 THE AMOEBAE LIVING IN MAN 



The earliest observations* on the division of E. histolytica appear to 

 have been made by Harris (1894), who saw division occur in the Hving 

 organisms. He saw several specimens divide into two, but gave very 

 imperfect figures. A division into three which he once saw was 

 doubtless a pathological process of fragmentation. According to 

 Harris's account, the daughter individuals remain attached for a time 

 b}^ a slender connecting thread of cytoplasm. I have never been able 

 — in spite of many attempts — to observe division in living specimens of 

 E. histolytica. Harris says he sought for it in vain for three years. He 

 finally saw it in the stools of only one patient suffering from acute 

 amoebic dysentery. At his first observation he saw one amoeba divide 

 into three; at a second he saw "several amoebae" divide into two ; 

 and at a third, "division was again observed" (into two?). No 

 cytological details were made out. 



It should be added here that the binucleate specimens of E. histo- 

 lytica, which sometimes occur in the stools, and which many observers 

 have seen and noted, are not normal division stages. They are, I 

 believe, forms which were undergoing division at the time when they 

 were passed out of the body, and in which nuclear division has then 

 been completed without fission of the cytoplasm following. As is well 

 known, the sudden cooling of cells or organisms during division usually 

 causes an arrest or regression of the process ; and the appearance of 

 binucleate individuals of E. histolytica in stools is probably to be 

 similarly explained as a result of the sudden change of temperature 

 experienced on leaving the host. These binucleate forms I have some- 

 times watched for a considerable time, but they have never completed 

 their division. 



Cutler (1919) has recently published an account of the division of 

 E. histolytica which is largely incorrect, and is based upon a study 

 of degenerate individuals in human stools — so far as I can judge. He 

 does not appear to have seen most of the stages which I have here 

 described. He believes that there is a peculiar " chromatin extrusion " 

 during the division of the nucleus ; but from his account it seems to me 

 probable that this is a degenerative phenomenon. Certainly no such 

 process occurs in the organisms which I have studied — nor in the 

 nuclear division of any other protozoon with which I am acquainted. 



A process of multiple fission or schizogony has been described in 

 ^^ Amoeba dysenteriae" (=E. histolytica) by Job and Hirtzmann (1916). 

 What their "morulae" supposed to be so formed really were I am 

 unable to decide from their description and figures. They certainly 

 were not stages in the normal development of E. Itistolytica, in any case, 

 as Mathis and Mercier (1916 h) have already pointed out. The whole 

 account is highly suspicious and unconvincing. More recently the 

 same authors (Job and Hirtzmann, 1919) have reafHrmed their belief in 

 the existence of a schizogony, but without adducing any evidence. 



Encystation. — Before the amoeboid forms of E. histolytica encyst they 

 undergo a reduction in size, with the formation of precystic individuals 



* Kruse and Pasquale (1894) figured what they thought might be dividing amoebae, 

 but they were unable to observe division. Their figure appears to depict either two 

 separate amoebae in contact, or else a couple of large cells from the stool. Doflein 

 (1901) suggested that these forms might be stages in "conjugation" — a suggestion 

 which seems quite unjustified at the present day. 



