PART II. CHARACTERS AND DIAGNOSIS 59 



condition of acute amoebic dysentery. Though this is probably the 

 commonest mode of onset of amoebic dysentery, in a certain number 

 of cases actual dysentery sets in soon after infection has taken place 

 without there having been a previous " carrier " period. This was 

 the experience of Walker and Sellards in their infection experi- 

 ments, where a small percentage of the men who became infected 

 had attacks of amoebic dysentery within a comparatively short time 

 (ten days or more) of ingesting the infective material. In cats, 

 again, it is usual for actual dysentery to occur without any inter- 

 vening " carrier" period; in fact, no one, as far as we are aware, 

 has yet produced a "carrier" condition in a cat without there having 

 been actual dysentery first. These primarily acute cases, as with 

 the cases of dysentery which are lapses from a " carrier" condition, 

 naturally clear up clinically without treatment, and pass into the 

 carrier condition, which must be looked upon as the most usual 

 normal type of infection with E. histolytica. 



The idea that a parasite should give rise in most cases to very 

 few or no symptoms at all in its host is not strange in any way and 

 is merely an indication of an adaptation of host and parasite to 

 each other, a condition of affairs which is, so to speak, the ideal 

 arrangement aimed at by a parasite. Any parasite which quickly 

 destroys its host is very soon likely to be destroyed itself. 



~E. histolytica infections may therefore be established in the 

 following ways after ingestion of the infective cysts : 



(1) The case may become a carrier case showing amoebae and 

 cysts in the stool without there having been any evidence of 

 previous dysentery and without any tendency to the development 

 of acute symptoms. 



(2) The case may have a primary attack of amoebic dysentery 

 and pass on into the carrier condition later. 



(3) The case may become a carrier and then lapse into a condi- 

 tion of amoebic dysentery only to become a carrier again as the 

 symptoms subside. 



As already mentioned above it is possible that the great majority 

 of carriers eventually show dysenteric symptoms, but as yet we 

 have a very few data to go upon. Actual amoebic dysentery is 

 essentially a chronic disease and persons who suffer from it are 

 constantly having attacks of dysentery alternating with periods of 

 freedom from the acute symptoms. During the attacks amoebae 

 with included red blood cells can be found in the stool while 

 between the attacks there occur cysts of E. histolytica and small 

 minuta amoebae. During the attacks the stools contain blood and 



