OEttEfeAL feACTEfelOLOGY 
37 
Certain bacteria produce the so-called coagulating, or 
“lab” ferments (from Latin lab , meaning rennet—a sub¬ 
stance found in the stomach, which coagulates milk) 
which causes coagulation of certain fluids, such as 
milk, blood, etc. Some bacteria produce fat-splitting 
ferments (cholera spirillum). 
As regards the fermentative properties of bacteria, 
the most important ferments are those which split the 
various sugars, cause the production of lactic acid, and 
the alcoholic fermentation (brought about by both 
bacteria and yeasts). 
A very important class of bacteria is that of denitrify¬ 
ing bacteria—those which reduce the protein decom¬ 
position products to nitrates in order that the plants 
might absorb nitrogen. 
The Anabolic (Upbuilding) Activities of Bacteria.— 
These consist in the property of some soil bacteria to 
accumulate large amounts of nitrogen from the air and 
thus to make up for the loss brought about by the ab¬ 
sorption of nitrogen by plants (Winogradsky). Even 
more important than this is the class of bacteria found 
in the root tubercles of certain plants (leguminosse), 
such as beans, peas, etc.; these bacteria not only do not 
withdraw nitrogen from the soil but enrich it, and 
upon this knowledge depends the well-known method 
of crop alternation used by farmers the world over. 
Certain bacteria bring about oxidation of ammonia 
to nitrites and pitrates; these are called nitrifying bac¬ 
teria. Some bacteria living in the salt water produce 
light, and a large number of bacteria (including the 
pathogenic bacteria) produce various pigments, thus 
staphylococcus aureus produces a yellow pigment, 
bacillus pyocyaneus produces a green pigment, while 
that produced by bacillus prodigiosus is red. 
