216 
Amoebae 
Giemsa’s stain they take a brownish or greenish colour, with iron- 
haematoxylin they are light yellow. 
The vegetative amoebae of this type seldom measure more than 12 /i. 
Many small forms are also found, measuring as little as 2 /a. The 
vegetative form (fig. 21) is generally very filmy and delicate, showing 
a faint hyaline plasma containing scattered granules without any 
definite distinction between ectoplasm and endoplasm. Pseudopodia are 
commonly single and rather broad and blunt; spinous pseudopodia 
were not seen in this form. The nucleus is generally hard to distinguish 
in unstained specimens but may appear as a faint pinkish circular area 
1-2 fx in diameter. One contractile vacuole is generally present in the 
active amoeba and contracts once in 25-70 seconds. Movement is, as 
a rule, more active than in type (a), the whole body gliding rapidly, 
often without any appreciable formation of pseudopodia. Fission has 
been observed in fresh specimens 24 times (figs. 22 and 23). The 
amoeba does not lose its motility and become condensed before fission 
as in type (a) but while actively motile it suddenly assumes a dumb-bell 
shape and divides into two daughter amoebae within one minute. The 
formation and detachment of a bud about 1-4 p, in diameter have 
been observed in fresh specimens on four occasions. Nothing has been 
observed in this strain approaching the formation of the lobulate bodies 
which are so characteristic in cultures of type (a), but, on the other 
hand, the following curious modifications of activity have been noticed. 
An active amoeba may suddenly become constricted in the middle, 
the two halves separating and giving a transitory appearance of fission : 
they, however, immediately come together again, the amoeba resuming 
its former habit. In the same w'ay a small portion of the amoeba may 
appear to separate off from the main body to become immediately 
reabsorbed. These appearances are suggestive of abortive fission and 
gemmation respectively. On two occasions in cultures of this tj^pe, a 
motile amoeba has been observed to become spherical and acquire 
a double contoured envelope. One of them was a daughter amoeba 
the product of fission one hour old when encystment commenced; in 
the other case the amoeba had given off a bud 35 minutes before. 
In stained specimens the vegetative forms have a diameter of 2-14 /x; 
the nucleus, which in a well grown form measures about 2 /x, stains le.ss 
intensely than in the amoeba of type (a ); osmic acid fixation followed 
by Giemsa staining fails to show a clear distinction between ectoplasm 
and endoplasm (fig. 25). Fission forms (fig. 27) and forms containing 
endogenous buds (fig. 26) are seen, as also vacuolated bodies wfithout 
