66 THE AMOEBAE LIVING IN MAN 



that the " minuta " amoebae give rise, in some way, to the cystic " ietragena 

 phase." Swellengrebel and Schiess (1917) even say that this pecuHar 

 development has been " demonstrated " ; but it appears to me to rest upon 

 a misconception of the part played by the precystic amoebae ui the life- 

 cycle of the parasite. 



As we have seen,* Kuenen and Swellengrebel (1913) have never 

 proved that the " minuta " forms are capable of living saprozoically, and 

 it is more than probable that they are not. So far as I understand their 

 views, they rest upon a misinterpretation of the following facts, which are 

 well known to everybody familiar with E. histolytica, (i) A patient 

 suffering from acute amoebic dysentery passes the large tissue-invading 

 forms of the parasite only (their "histolytica phase"), and not precystic 

 amoebae or cysts. (2) Wlien the symptoms abate, the patient suffers from 

 diarrhoea, and passes chiefly precystic amoebae (their "minuta phase"). 

 (3) When the symptoms disappear, and the patient's stools become solid, 

 he passes cysts only (their " tetragena phase "). All these events are very 

 simply explained — as I have already shown — without having recourse to 

 their hypothesis. In the ordinary carrier of £. histolytica all the " phases " 

 actually exist simultaneously. The cysts are in his stools ; the precj^stic 

 amoebae are in the lumen of his gut— from which they can easily be 

 obtained at any time by the administration of a purgative ; and the tissue- 

 invading forms are in the ulcers in his gut wall — from which they could be 

 obtained by scraping the ulcers, though not, as a rule, by the administra- 

 tion of purgatives. I do not know how Kuenen and Swellengrebel 

 account for the appearance of large numbers of cysts in the faeces of a 

 carrier every day for long periods, unless they suppose that the cysts 

 multiply in the large intestine : nor how they would account for the fact 

 that the carrier has an ulcerated intestine containing parasites of 

 " histolytica " form ; nor yet how they would explain the case of a carrier 

 with " tetragena phase " cysts in his faeces, an abscess full of " histolytica 

 phase " amoebae in his liver, and " minuta phase " parasites discoverable 

 in his stools as often as a purgative is administered to him. But their 

 hypothesis will require much fuiiher elaboration and far more evidence 

 than they have hitherto adduced if it is to explain the facts and gain any 

 adherents. At present I cannot find any evidence in favour of it in the 

 publications of Kuenen and Swellengrebel (1913, 1914), Swellengrebel 

 and Schiess (1917), or any other workers. 



Another peculiar interpretation of the life-cycleof £. histolytica is that 

 put forward by Mathis and Mercier (1916). These authors, who call the 

 parasite E. dysenteriae, believe that it occurs in three chief " forms " or 

 "types," — a "tetragena form," free in the gut; an encysted form, in 

 normal stools ; and a " histolytica form " in dysenteric stools. Of the 

 last they say : " The fact that the histolytica type is seen exclusively in the 

 bloody mucous stools of acute attacks of amoebiasis, allows us to admit 

 that this type does not belong to the developmental cycle of the parasite." 

 And they conclude — if I understand them correctly — that the ordinary 

 forms of E. histolytica, which occur in all the tissues capable of invasion, 

 and which constitute the major part of the species, are a kind of 

 developmental abnormality. Their reasons for taking tliis curious view 

 are not clear to me : and consequently, beyond noting that their use of 

 the terms " histolytica " and " tetragena" seem to have but little historic 



* See p. 61 ei seq. 



