8 PROTISTS AND DISEASE 



It is as if a new " Third Kingdom " were being erected 

 to replace that of the Monera. Just as there are cytodic 

 (plasson, chromidial) stages of some protists which have 

 obvious nuclei at other stages, so there are filtrable stages of 

 parasites such as molluscum corpuscles, which are relatively 

 large bodies; and, just as some living organisms may con- 

 ceivably be persistently akaryote, so others may possibly 

 exist only in the filtrable phase. 



Protoplasmic Motion. " The colloidal nature of proto- 

 plasm is manifested in many of its properties. Its power of 

 adsorption which lies at the basis of many cell reactions and 

 certain staining processes, is similar to that of other colloids. 

 . . . The permeability of a vacuolate cell is in general the 

 resultant of the permeabilities of the ectoplast, cytoplasm, 

 and tonoplast" (L. W. Sharp, 1921). The chief cause of 

 stability in colloids is Brownian movement (Bayliss, 1920, 

 q.v.). This movement is seen in many living cells, e.g. in 

 the protoplasmic strands of Spirogyra. Streaming is probably 

 present in the protoplasm of all active cells. It was first 

 recorded in Chara by Corti in 1774. In some cases, as in 

 the cells of the stamina! hairs of Trad-escantia, the stream 

 does not carry the nucleus with it ; in other cases, as in the 

 leaves of Vallisneria, the nucleus moves with the rest of the 

 protoplast. 



Most impressive are the to-and-fro currents of the 

 plasmodium of Mycetozoa : in these the outward current 

 lasts over a minute, the return a little under a minute. In 



