1901) MICROSCOPICAL JOURNAL. 3U5 
the embryo-sac, These are (a) the ‘‘definitive nucleus,” 
(b) the “synergide” and egg-cell at the micropylar end of 
the sac, and (c) the “antipodal cells,” three in number, at 
the opposite end. In the definitive nucleus we easily 
make out the nuclear membrane, the chromatin masses, 
and the large nucleolus. The latter has a well-defined 
border, and moreover this border is seen to be of fair 
thickness, and may at certain points be depressed to- 
wards the interior, which is clearer. Obviously in this » 
case the nucleolus has the structure of a vesicle, and it is 
probable that all nucleoli are of this nature, being filled 
with a clear fluid of an oily consistency. —Science-Gossip. 
THERMAL DEatTH-PoInTs OF BacTERIA.—Different species 
of bacteria vary greatly in their powers of resisting the 
action of heat. Speaking generally, pathogenic micro- 
organisms perish at a much lower temperature than non- 
pathogenic bacteria. Thus the well-known B. prodigiosus, 
which forms a beautiful blood-red colony when grown on 
moist bread, cannot withstand a temperature of 58° C. 
for more than ten minutes, whereas the tetanus bacillus 
only perishes after six hours at 80° C. The bacillus of 
tuberculosis is rapidly destroyed in cultivations at 70° to 
80° C.; but according to Welch, it can resist in the dry 
state a temperature of 100° C. for three hours. In milk 
it has been found to perish after four hours at 55° C.; 
one. hour, at 60° C.; five minutes, at 80° C.; and one 
minute, at 95° C. (Forster). The spores of bacteria can 
_ withstand far higher temperatures than the bacteria them- 
selves. Thus the spores of the tetanus and anthrax ba- 
cilli are both extremely resistant to heat, though the lat- 
ter are destroyed by moist heat at 90° to 95° C. This 
fact is recognized in the sterilization of food products, 
which are first heated to a sufficient temperature to de- 
stroy the parent bacteria, then left for the spores to de- 
velop, and again heated to kill the newly-formed bacteria. 
