72 PROTOPLASM OF PROTOZOA 



under side of the surface film of water, creeping on this as though it 

 were a sohd body, but Bles (1929) denies that Arcella can move on a 

 clean surface film. Specimens of Amoeba on the under side of the cover 

 glass swell up when disturbed, but may still stay attached to the "ceil- 

 ing" (Bellinger, 1906). Adhesion to the substratum, according to 

 Mast (1926b), is due either to the secretion of an adhesive substance or 

 to a state of the plasmalemma. According to Rhumbler (1898) and 

 Jennings (1904), an amoeba probably adheres to the substratum by a 

 mucus-like secretion. Many observers have reported that if the surface 

 of an amoeba is touched with a fine glass rod, it adheres to the glass 

 rod, so that sometimes a bit of the organism may be pulled off (Mast, 

 1926b) or the whole organism may be dragged about by a thread of 

 mucus from the amoeba which has become attached to the glass rod 

 (Rhumbler, 1898; Jennings, 1904). According to Chambers (1924), a 

 stationary amoeba accumulates a considerable amount of slime, by 

 which it is attached to the substratum; an amoeba dragged out of posi- 

 tion and then released will be pulled back toward its original position. 

 However, Schaeffer (1920) has not been able to convince himself that 

 amoebae secrete mucus; nevertheless, whatever the method, the tips of the 

 pseudopods often adhere so firmly to the substratum that strong squirts 

 from a pipette are necessary to dislodge them (Bellinger, 1906). Hy- 

 man (1917) applied a needle to the posterior end of an amoeba and 

 pulled the animal in two, in spite of the tensile strength of the ecto- 

 plasm. 



It is commonly held that attachment is one of the important factors 

 in ameboid movement: when the organism is not attached there is no 

 locomotion, although protoplasmic flow and the gel-sol and the sol-gel 

 processes may be observed. Mast (1929) has studied the factors in- 

 volved in attachment of A?7ioeba to the substratum and finds that simple 

 agitation of the dish in which the amoeba are cultured may cause an in- 

 crease in the firmness of adhesion. There was slight attachment in pure 

 water (see also Parsons, 1926), but strong attachment over a great 

 range of hydrogen-ion concentration, p\l 4.6 to 7.8). All the salts 

 tested by Mast caused a decrease in time for attachment, and an increase 

 in firmness of attachment; since non-electrolytes have no eff^ect, Mast 

 believes that charges on the ions may change the surface charge of the 

 amoeba or may change unknown internal forces. Bles (1929) has shown 



