38 THE AMOEBAE LIVING IN MAN 



exactly comparable with the bacillary "carriers" of various sorts. It 

 is, perhaps, unfortunate that the same term should have been employed 

 for both ; but since it is in current use, it seems inadvisable to try to 

 change it now. 



We can now see that the carrier of E. histolytica is merely the 

 ordinary individual in the normal state of infection. He is the indi- 

 vidual who is naturally adapted to his parasites, and who suffers no 

 appreciable harm from their presence. From the diagnostic point of 

 view, he is the individual who passes the cysts of the amoeba in his 

 stools. If the amoebae do him no harm, and find his bowel a comfort- 

 able environment in consequence, they develop in their normal manner 

 — completing their life-cycle by encystation. The carrier of E. histolytica 

 can therefore be accurately defined as the individual who passes cysts 

 of the parasite in his stools. 



The carrier obviously "carries" the active amoebae in his tissues. 

 He is a carrier of amoebae. He is not properly called a "cyst-carrier" 

 — a term which has unfortunately been introduced into many languages, 

 and which is now used by many workers — because he does not " carry " 

 cysts* in any ordinary sense. He deposits cysts as soon as they are 

 formed. Nobody would call a man infected with an intestinal worm an 

 " egg-carrier" : because if he "carries" anything, it is clearly the worm, 

 — not the eggs which it lays and which he discharges in his stools. 

 " Cyst-carrier " is similarly a misnomer, and does not correctly represent 

 the facts. 



Walker (191 3) divides carriers into two classes — contact carriers and 

 convalescent carriers. The former are those people who have never 

 suffered from amoebic dysentery ; the latter, those who have had an 

 attack of amoebic dysentery, but who have then recovered clinically 

 without losing their infections. On clinical grounds it is important to 

 recognize these two categories ; for the contact carrier is typically a 

 healthy individual, whose infection does him no appreciable harm, 

 while the convalescent carrier is the individual who has shown himself 

 susceptible to the action of the parasite. He has already suffered, and 

 frequently continues to suffer, from their presence. Clinically, he is 

 often a case of relapsing dysentery, with intermissions of variable 

 duration when he passes into the carrier state. There is, of course, 

 no hard and fast line between the typically healthy carrier and the 

 patient suffering from acute amoebic dysentery. They are the extreme 

 manifestations of one common condition — intestinal amoebiasis — con- 

 nected by all intermediate states, any of which may be seen in different 

 individuals or in the same individual at different times. 



Carriers are of importance from two different standpoints : the 

 practical, because they alone are the source of infection to others ; the 

 theoretical, because they explain all the apparent contradictions which 

 previously prevented people from understanding the part which E. histo- 

 lytica plays in the causation of amoebic dysentery. It is now easy to 

 understand — though unfortunately still not generally understood — how 



* We even read, in recent papers, of carriers oi E. histolytica being "infected with 

 cysts." This shows a most incomprehensible ignorance of the true conditions. It is 

 doubtless due to the same confusion of ideas that leads people to talk of "cyst-carriers," 

 and to ask for methods of treatment that will enable them to "kill the cysts" inside 

 an infected person. 



