312 



PLASMODROMAtA AND SARCODINA 



Morphology. — It is usually about 25 to 40 fi in diameter, but may 

 be as small as 20 ju, 10 ju, or even 5 ju. When at rest it is spherical, 

 but varies in shape when in motion. The ectoplasm is usually 

 well defined, and in pseudopodia is seen to consist of hyaline highly 

 refractive protoplasm, but this differentiation is sometimes difficult 

 to define. The endoplasm is greyish in colour, and usually contains 

 red blood-corpuscles as well as other matters. The vesicular 

 nucleus is clearly visible, and has a well-defined membrane on which 

 chromatic granules are distributed. In the centre there is a karyo- 

 some surrounded by a clear area, and containing a centrosome. 

 A cycle of changes is constantly proceeding in the nucleus: first 

 chromidia break away from the karyosome and pass outwards into 

 the nucleus, and this proceeds until little but the centrosome is 

 left, when it ceases, and chromatin begins to accumulate again 

 around the centrosome, until the karyosome is re-formed, when the 

 cycle begins again. 



Life History. — ^Asexual reproduction is by promitosis. Sporogony 

 is rare, and when it occurs tends to cyst formation, before which 

 the amoebae become small, and their chromidia form three to six 

 masses. The cyst sometimes contains a large vacuole. Nuclear 

 division takes place until four nuclei are formed. The further 

 life-history is unknown. 



In 1912 Calkins gave his account of the Genera and Species of 

 Amoebae, Hassall his valuable bibliography, Crawley his list of 

 Parasitic Amoebae, Craig his relationship of Parasitic Amoebae to 

 Disease, Darling his identification of Pathogenic Panama Amoebae, 

 and von Prowazek the structure of the nucleus of parasitic Amoebae, 

 while James contributed two papers on the clinical identification 

 of the Entamoebae and on infection with E. tetragena. In the latter 

 of these papers it is stated that the histolytica phase is found in 

 infections with acute symptoms, while the tetragena phase is found 

 in more chronic infections. Craig formulates a life-history for 

 L. histolytica as follows:— 



1. Vegetative Stage: Histolytica-phase in acute dysentery; 



tetragena-phase in chronic dysentery. 



2. Precystic Stage : Amoebae decrease in size (minuta-phase), 



and the nucleus is intermediate in type between the other 

 two phases. 



3. Cystic Stage : Cysts 7-20 microns quadrinucleate. 



In 1 913 Whitmore gives an account of his own and the work of 

 Viereck, Hartmann, and Huber. In 1914 there appeared a most 

 important paper by James detailing historical matter, morphology, 

 and classification and technique, with regard to the Entamoebae of 

 man. In 191 7 Craig gave an excellent summary of the Amoebae 

 parasitic in man. 



We thus see that although L. coli and L. histolytica are distinct, 

 it is difficult to effect a diagnosis in the trophozoite phase, and that 

 histolytica, tetragena, and perhaps minuta, are phases of one and 

 the same organism. 



