402 SPECIFIC MICRO-ORGANISMS 



placed. Binary division with mitosis of the nucleus seems to be 

 the common mode of multiplication. Multiple division also 

 occurs in the vegetative state. The resistant stage (cyst) is charac- 

 terized by a thick, firm wall of several layers, within which the 

 nucleus divides into 200 or more daughter nuclei. Each of these 

 becomes surrounded by a little cytoplasm and, when the cyst 

 bursts, wanders out as a young ameba. The life history is in- 

 completely known. 



Cultures of saprophytic amebae are readily obtained upon 

 agar plates. The medium contains agar 0.5 gram, tap water 



FIG. 173. Eutamceba coli. a, Free ameba; b, ripe cyst with eight nuclei. (From 



Doflein after Hartmann.) 



90 c.c., ordinary nutrient broth 10 c.c. Cultures are incubated 

 at 25 C. Williams 1 has succeeded in obtaining pure cultures, 

 free from bacteria, at 36 C. by employing agar smeared with 

 naturally sterile brain substance. 



Entamoeba Coli. Loesch 2 in 1875 observed amebae in the 

 human large intestine in gastro-intestinal disturbance. The 

 organism is very common in the human intestine, being found in 

 10 to 60 per cent of persons without digestive disturbances, 

 when the examination is thorough. 



The cell in the vegetative stage is variable in shape and size, 



1 Journ. Med. Rsch., 1911, Vol. XXV, pp. 263-283. 



2 Virchow's Archiv, 1875, Bd. LXV, S. 196-211. 





