18 PARASITIC AMOEBAE OF MAN. 



may be present, of large size. In the parasitic species 

 found in man, vacuoles are generally present and are 

 digestive in character, but they are never observed to 

 pulsate. Small masses of granular material are often 

 seen within the vacuoles and sometimes stain with 

 neutral red, thus showing that the vacuoles are diges- 

 tive in character. As a rule the vacuoles are situated 

 near the periphery of the amoeba?, especially when they 

 are contractile, but they change their position with the 

 movements of the organism. In Amoeba proteus, a 

 free-living form, it is easy to observe the formation 

 and contraction of the vacuole. At first it is situated 

 near the nucleus and is very small, but as nutritive ma- 

 terial collects within it, the vacuole grows larger, at 

 the same time moving toward the periphery of the 

 organism. When it arrives at the periphery it sud- 

 denly contracts and its contents are rejected from 

 the body of the amoeba. Such phenomena are never 

 observed in the parasitic amoebae of man. 



In addition to the vacuoles there are present in 

 the endoplasm of some species of amoeba*, especially 

 those parasitic in man, numerous minute, oval or 

 round bodies, which resemble the spores of malarial 

 plasmodia, in unstained preparations, and which have 

 been described by different authors as spores. At a 

 certain stage of the development of Entamceba coli, 

 several such bodies may be observed in both living and 



