70 



GENERAL BIOLOGY 



observing them later; else, the following observ^ations will 

 not be possible : for if they be cooled, they will contract into 

 a heap, and remain inactive and scarcely recognizable. 

 Therefore, the air of the room in which they are studied, and 

 the slide and cover and stage of the microscope must not 

 be cooler than the water from which they are taken. 



In a few moments after their transfer to the slide (the 

 drop being properly covered, and the space beneath the 

 coverglass entirely filled with water) the amoebas should be- 

 gin to creep around freely upon the sur- 

 face of the glass. Although very minute 

 they will be recognized even under low 

 power by their form (see fig. 51) and 

 especially by their slowly changing out- 

 lines. The details of internal struc- 

 ture in a single animal are not to be ob- 

 served except with high magnification, 

 and a sufficient cutting down of the light 

 to allow the more transparent parts of 

 the animal to come into view. When 

 found and properly lighted, it will be easy 

 to recognize in the body a granular cen- 

 tral mass of protoplasm, a clearer exterior layer, with 

 definite, though slowly changing outline that never shows 

 sharp angles, but only rounded lobes. 



The granular internal portion of the body of the animal 

 is spoken of as the endosarc. Within it are to be seen 

 i) the round and uniformly translucent nucleus: 2) the 

 very clear contractile vacuole, which disappears at intervals, 

 and which usually shows a tinge of pinkish color, and 

 3) ingested food particles, usually aggregated more or less 

 into round food balls which may be seen moving about in 

 the endosarc. In these food balls the forms of some of 

 the bacteria more recently eaten may usually be recognized^ 



Fig. 51. Amoeba, a, 

 an active individ- 

 ual; ps, pseudopo- 

 dium; m, nucleus;/, 

 food; V, vacuole; 

 b, diagrammatic 

 representation of 

 division. 



