THE FUNGI 2438 
for an hour to a temperature of 149°-160° Fahrenheit 
(65°-71° C.). The spores resist a much greater heat. 
Light is unfavorable to the growth of bacteria in gen- 
eral, and this is one important reason why living rooms 
should be open to the sunshine. 
Dryness will not immediately kill bacteria, but it stops 
their growth, and it is for this reason that evaporated fruits 
and vegetables keep without decaying. In the case of 
salted meats and fish, either smoked or not, the dryness 
and the presence of 
much salt prevent decay. 
Smoking adds some cre- 
osote which is an addi- ,' ¥ 
tional safeguard. Most 
bacteria cannot grow in 
the presence of much 
sugar or of vinegar, and 
this accounts for the 
keeping qualities of rich 
preserves and jellies as 
Fic. 170. Effect of Variations in Tem- 
perature on Bacteria Growth. 
a, a single bacterium; 0, its progeny in 
well as of pickles. twenty-four hours at 50° Fahrenheit; 
. c, its progeny in twenty-four hours at 
312. Reproduction. Tie Palaonnett 
Bacteria under ordinary 
circumstances reproduce by the division of the cells, each 
parent cell forming two new ones. From this fact they 
are often called fission fungi. Fission goes on much faster 
at rather high temperatures (Fig. 170). Resting spores 
are formed by many species. The process of spore forma- 
tion consists of the interior portion of the protoplasm 
collecting into a minute ellipsoidal or globular mass which 
becomes surrounded by a thick membrane. The spores 
‘ean survive high temperatures and extreme dryness, so 
