1060 PATHOGENIC PROTOZOA 



from an infected animal which has been killed and making serial 

 sections of the ulcers. In such sections it can be seen that the 

 chromatin of the nucleus migrates from the nuclear membrane to- 

 ward the center, and the nucleus elongates, being first oval and 

 later spindle shaped; although the chromatin dots and threads and 

 the achromatic fibers can be readily seen in the well stained speci- 

 mens they do not show the usual typical figures of a typical mitosis, 

 but are arranged in an atypical and irregular manner. The elongated 

 nucleus becomes constricted in the middle and a little later divides 

 and the cytoplasm soon follows, leaving two daughter cells. 



Degenerative Forms. These are extremely common in stale 

 stools, in cases during convalescence, or under active treatment, and 

 also in experimental dysentery in the cat, and they have led to 

 much confusion in the past. The nucleus breaks up into fragments 

 and chromatin masses are extruded into the cytoplasm in irregular 

 forms, and parts of the cells are apparently budded off. At one 

 time the budding process was looked upon as normal by Schaudinn 

 and his followers, but there is now little doubt that both spores 

 and buds are degenerative changes and that the animal multiplies 

 only by binary fission in the vegetative forms or by the development 

 of four nuclei in the cysis. 



Cyst Formation. The encystment follows the general rule in 

 that under suitable conditions, an amoeba comes to rest, ejects all 

 food particles from the cytoplasm which becomes finally granular, 

 and round, and then secretes a cyst wall, and in this condition 

 passes out of the body with the feces. The cyst of Entamoeba his- 

 tolytica was first described by Quincke and Roos (1903), and again 

 by Huber (1903), but without making any real impression on the 

 medical or zoological opinion of the day. They were redis- 

 covered by Viereck (1907) and called by him Entamoeba tetra- 

 gena, and for a time was believed to be a new species. In fact, Hart- 

 mann described a vegetative stage of Entamoeba tetragena as Ent- 

 amoeba africana, afterwards accepting the name "tetragena," but 

 it is now apparent that tetragena is merely the end, or cyst stage, 

 of Entamceba histolytica, which had formerly been overlooked by 

 Schaudinn and his followers. Cysts are not easily found in all cases, 

 and it is possible that when treatment is vigorous they never develop. 

 They are, without doubt, the form in which 'the parasite leaves the 

 body to infect new victims; because of their heavy cyst wall they 

 are quite resistant. The protoplasm of the cyst and the precystic 



