R. T. Wells 
209 
ture of 25° C. Examining such a slide culture under the low power, 
one picks out a spot towards the tail end of the inoculation stroke 
where the cysts are thinly scattered; a single one is then isolated 
under the oil-immersion lens for continuous observation. 
For permanent preparations fixation after the method of v. Wasie- 
lewski and Hirschfeld (1909) gave the best results. The principal 
fixatives used were osmic acid (2 “/o) ^^d corrosive-acetic-alcohol, 
followed by Giemsa’s stain and iron-haematoxylin-eosin respectively. 
The first method of fixation gives the best picture of the plasma, the 
second brings out the nuclear material particularly well. 
III. Morphology and life-cycle of the amoebae. 
A reference to the table shows that, in 12 out of the 14 growths 
of amoebae obtained from the air in the manner described, two types 
of cysts were distinguished. The following description is concerned 
only with the growths of amoebae occurring on one single plate 
(No. 24 with table). 
Cysts of type (a) (PI. VI, fig. 1), have a diameter of 8-14, generally 
10-12 /u,; their shape is round, oval, more frequently trihedral, poly¬ 
gonal or stellate; the wall is about 0‘25 g in thickness and has a 
strongly marked double contour; the outer layer is generally wrinkled, 
reminding one of the outline of an Ascaris ovum. The plasma is 
compact and coarsely granular and a circular or oval eccentric nucleus 
is, as a rule, more or less distinctly visible in unstained specimens. 
Cysts of type (6) (PI. VI, fig. 19) on the other hand, are much smallei’, 
having a diameter of 3-8 g] the shape is round or oval, with little 
or no tendency towards the modified forms often assumed by cysts 
of type (a); the surface is smooth and the wall delicate with a faint 
double contour. The plasma is hyaline with thinly scattered highly 
retractile granules ; a nucleus is hardly to be distinguished. 
Cysts of both types stain an intense purple black with iron- 
haematoxylin. 
In order to determine whether these two well defined types of 
cysts represent two different species or simply polymorphic forms 
belonging to a single species, attempts were made to obtain cultures 
originating from a single cyst of each type by Walker’s method, as 
above described. In many cases however the cysts isolated failed to 
germinate; it was therefore found more practicable to select a single 
motile individual as the starting point of a strain. 
14—2 
