308 THE PROTOZOA 



of Oscillaria is rolled up into a small coil, and considerable space is 

 thus saved. An Amoeba, 90 /j. in length, absorbed and coiled up a 

 filament of Oscillaria 540 p long. Quite similarly, a drop of water 

 quickly draws into its substance a minute splinter of wood or glass, 

 while all fluids show the same power in respect to certain substances. 

 A drop of chloroform will draw in a shellac thread from the surround- 

 in°- water, and will roll it up within its substance in exactly the same 

 way that an Amceba rolls up a filament of Oscillai'ia (Fig. 153, B, C). 

 Egg albumin and gum arabic in solution show the same phenomenon, 

 the rapidity of ingestion depending upon the density of the medium. 

 To a physicist such a process is explained by the phenomena of 

 cohesion and adhesion; the coefficient of adhesion between the chloro- 

 form and the shellac filament is greater than the coefficient between 

 shellac and water. But if a splinter of glass be mechanically inserted 

 in a drop of chloroform suspended in water, the splinter will quickly 

 leave the chloroform and seek the water. In this case the coefficient 

 between glass and water is greater than that between glass and chlo- 

 roform. Rhumbler tried the ingenious experiment of coating a glass 

 splinter with a layer of shellac ; when one end was placed against the 

 chloroform drop, the splinter and shellac were quickly drawn into the 

 drop. Here the shellac was soon dissolved by the chloroform, and 

 the splinter was gradually left naked, whereupon it soon left the drop, 

 being drawn into the surrounding water by reason of the greater 

 coefficient of adhesion between glass and water. Here, according to 

 Rhumbler, is an analogue of the process of feeding on the part of 

 Rhizopoda. Bodies are ingested into the plasm because of the greater 

 attraction to the fluid protoplasm than to water, then, through the 

 chemical changes between protoplasm and the digestible parts of the 

 foreign substances, the constituents of the foreign body are changed, 

 and a corresponding change is wrought in the attractive force which 

 keeps them together, that is, in the coefficient of adhesion, and defe- 

 cation results. 



Similarly with shell-formation, it has been shown by Vervvorn, 

 Dreyer, Rhumbler, and others, that Rhizopoda pick up all sorts of 

 foreign particles and excrete them at certain times upon the outside. 

 Rhumbler found that the same process may be repeated by inorganic 

 liquids, some of which {e.g. chloroform) show a selective tendency 

 in picking up some objects and leaving others, while Verworn has 

 shown that Amoeba will not pick up certain objects unless the latter 

 be made to irritate it so that a slimy secretion is poured out. In those 

 forms of Rhizopoda which appear to. select their building material, 

 the selection is often due to the character of the material at their 

 disposal, and partly to purely physical conditions, such as the ex- 

 clusion of large sand grains because of the small mouth opening, or 



