414 MANUAL OF BACTERIOLOGY. 



by the retraction of this thread which thickens as it shortens. 

 The cells may pull apart and be drawn together again by this 

 thread of protoplasm several times in the course of an hour. 

 Division of the nucleus is in some cases typically amniotic. 

 By dropping cover-glasses in fixing fluid at various stages of 

 the process certain stages can be studied. The encystment 

 mentioned above takes place sooner or later in all culture after 

 longer or sorter period of multiplication and independently 

 of the amount of moisture, but drying out hastens the proc- 

 ess. Encysted amebae transplanted to fresh culture-medium 

 usually begins to show signs of awakening activity in twenty- 

 four hours. These consist of agitation of the granules of the 

 protoplasm, and finally pulsation of the vacuole. If too much 

 of the old bacterial growth is transplanted on to the fresh 

 culture medium, the cysts may fail to germinate. No multi- 

 plication takes place within the cyst. The ameba leaves the 

 cyst behind as an empty shell. 



Spore Formation. Spore formation in amebae takes place 

 usually within 48-72 hours after they are transplanted to 

 fresh medium; but it varies as to time in different species. 

 They first appear as fine, brightly refractive granules, which 

 become larger and larger, by the aggregation of chromidia 

 or by becoming surrounded by a layer of cytoplasm until they 

 may become as large as the nucleus, and in fact have been 

 mistaken by some observers for multiple nuclei. The spores 

 vary in size from .7 to 2 mikra, and they stain faintly and 

 are more readily decolorized than the amebae. They are 

 extruded from the ameba in 24-48 hours from the time of 

 tHeir first appearance, but an ameba may become encysted 

 before the spores are extruded which has probably led to 

 the error of supposing that the encysted ameba may form 

 spores. The development of the spore into the ameba is 

 direct; the thickening of the wall described by some does not 

 take place if the conditions of growth are favorable. The 



