ENTAMCEBA HISTOLYTICA 189 



dysenteric type. If the extension is not rapid, then only occasional plugs 

 of mucus, which may or may not be contaminated with blood, are passed, 

 and the individual may be quite unaware of his condition. The cases 

 of rapid extension are regarded as the acute ones, and the amoebae are 

 all of the large tissue-invading form, many of which contain red blood- 

 corpuscles. In other cases, where there is not rapid extension, though 

 a considerable area of the wall must be involved owing to the enormous 

 number of amoebae or their cysts which are passed in the faeces, a state 

 known as the " carrier condition " occurs. Exactly what happens in this 

 condition is not properly understood, for it is difficult to obtain perfectly 

 fresh post-mortem material from these cases. It is not possible to repro- 

 duce the carrier condition in animals, which always acquire an acute 

 infection which either terminates fatally or disappears. From what can 

 be observed in the stool, it is found that a smaller type of amceba occurs 

 in the faeces of carrier cases. These are in reality encysting forms (pre- 

 cystic amoebae), for in association with them are to be found cysts showing 

 one, two, or four nuclei. In some cases the precystic amoebae and the 

 encysted forms are passed together in the stool, while in others only the 

 amoebae or only the cysts are passed. This is probably dependent upon 

 the varying rate at which the large intestine evacuates itself. It seems 

 probable that the small amoebae arise in the ulcers by division from the 

 larger tissue-invading forms under certain conditions which may be 

 supposed to hinder their free and easy development. As a general state- 

 ment it can be accepted that Protozoa encyst when the conditions of life 

 are becoming unfavourable. The small precystic amoebae are formed 

 from the large ones which have become more superficial in position, and 

 it might be surmised that if the large amoebae which have escaped from 

 the tissues into the debris which fills the ulcer remain there for some time, 

 as they may be supposed to do in the slowly extending cases, no increase 

 in size occurs through lack of proper food, though they multiply and give 

 rise at each division to increasingly small forms. These amoebae, deprived 

 of their proper food, which is to be found only in the tissues in the deeper 

 parts of the ulcer, become encysted, and escape into the lumen of the 

 intestine when the ulcer discharges its contents. This discharge may 

 take place before actual encystment is complete, in which case the small 

 precystic amoebae will be found in the stool. In certain cases enormous 

 numbers of cysts are passed in the stool, and it must be supposed that 

 the process described occurs simultaneously at many parts of the intestine, 

 not necessarily in large evident ulcers, but in the very small superficial 

 ones which are not readily detected by the naked eye. The lesions in 

 these cases may be merely superficial, and, not being of an acute nature, 

 it is not surprising that certain individuals may be passing extraordinarily 



