WHAT ARE MICROORGANISMS 9 
slightly elongated (Fig. 4, a). They form no mycelium and 
cannot force their way into hard substances. Their chief char- 
acteristic is their method of reproduction by a process called 
budding. ‘There appears on the side of the yeast cell a minute 
bud, which continues to increase in size until it becomes as large 
as the cell from which it has grown. Then the 
two cells may break apart at once; or each may 
in turn produce buds before they separate. 
In either case, two or more cells are produced 
from the one, and although they may remain 
attached so as to form irregular masses of = 
several cells (Fig. 4, 6), each cell is reallycom- pig. 4 —Yeast 
plete in itself . Eventually they break apart. ? on ver seomth te 
This budding takes place rapidly, though not budding. ¢, single 
so rapidly as the division of bacteria, which ‘°US:® Pudding cells. 
will be mentioned later. 
A second important character of yeasts is the nature of the 
fermentation they produce. They have an action especially upon 
sugars, which they break up into carbonic acid and alcohol. This 
action makes them play a large part in nature’s processes, quite 
O C) distinct from that of bacteria. 
Any further classification of yeasts is quite 
CD CD unnecessary for our purposes. 
3. Schizomycetes (Fission Fungi, or Bacteria). 
OO —This group comprises the bacteria proper; it is 
certainly the most abundant of the three, and in 
soteg uae; some respects it is the most important. It is 
of iivision by with the bacteria that we are chiefly concerned 
in this work. Bacteria have sometimes much the 
same shape as yeasts. The chief distinction between them is 
their method of multiplication. Instead of budding they multi- 
ply by fission. The bacterium elongates a little, and then 
divides into two equal halves at once (Fig. 5). Hence the name 
fission fungi. Bacteria are also, as a rule, smaller than yeasts, 
