410 DORIS L. MACKINNON. 
Study of this table shows that during my observations 
Culture B underwent two periods of deep depression, when 
no cysts were formed. From such a depression the culture 
recovered till the maximum of “ encystability ” was reached, 
when it again degenerated. 
Abnormality almest always showed itself first in the cold 
side of the culture; which suggests that a lowered tempera- 
ture weakens the resistance of the organism to unfavourable 
internal conditions. That lowered temperature has some 
paralysing effect on the ordinary cell-functions is further 
borne out by the much greater length of time required to 
elapse before encystation begins in a cold culture, and by the. 
relative slowness with which the successive stages are reached 
in it. The following table illustrates this :— 
Gane First day of Date of beginning of encystation. 
: starvation. In the warmth. In the cold. 
Bs . iI4th May ~~ loth May 72 = 20th May, 
1G) ig dlishiln) ig, = 2 OGle a. ~ ZA hee 
IG 5 Ail 2 Ohi . oth June 
Su ace ROLLSU ey . Ist June voy ecatlleaees 
That is to say, encystation usually sets in within forty-eight 
hours in the warmth, but not until four or five days later in 
the cold. 
The primary cysts afforded the most favourable material | 
for observation, as in this stage the silica-coat had not yet 
developed to great thickness. I fixed the primary cysts then 
with picro-acetic acid, stained them with borax carmine, and 
cleared them with clove-oil. In nearly every case in culture 
B 9, which was the one I used for taking measurements, the 
primary nuclei had already divided into secondary nuclei, 
though division into secondary cysts had not yet begun: fre- 
quently, however, the nuclei had become heteropolar. Suc- 
cessful preparation showed the cytoplasm stained a faint rose- 
colour, while the outlines of the nuclei, and even their finer 
internal structure, shone quite clearly through the silica coat. 
When the cysts were no longer normal, the excessive deve- 
lopment of silica made this clear view impossible. 
