Soiiv Changes Produced By Micro-organisms. 15 
action of the last two is spoken of as “Nitrification.” For the pres¬ 
ent, we shall confine our attention to ammonification. 
Like the higher plants and animals, bacteria must have their 
food in a liquid condition before it can be assimilated. In order to 
facilitate the solution of the complex proteids from which the am¬ 
monifying bacteria derive their nourishment, certain digestive en¬ 
zymes, similar to pepsin and trypsin in animals, are secreted by 
the tiny cells. As a result, the protein compounds are broken down 
first into albumoses and then peptones, the latter being soluble and 
consequently in a form which bacteria can use for food. From these 
peptones, amino acids are formed which themselves serve as food 
and ultimately give rise to ammonia and carbon dioxide. The en¬ 
zyme which is responsible for this digestion is known as a pro¬ 
teolytic or peptonizing ferment since it is capable of changing pro¬ 
teids into peptones. 
Bacteria which grow best in the absence of air (oxygen), 
known as anaerobes, are believed to play an important part in the 
early stages of putrefactive decomposition, and it is to their activi¬ 
ties that we must charge most of the malodorous gas formation 
which accompanies decay. 
Now, while the bacteria are busily engaged in decomposing 
nitrogenous material whereby their existence is maintained, a large 
number of substances of little or no value to them are split off 
from the complex nitrogen molecule. These are known as cleav¬ 
age or by-products. Again, during the growth and metabolism of 
the micro-organisms themselves, various waste products are ex¬ 
creted from their cells. The disagreeable and peculiarly character¬ 
istic odors evolved during putrefaction and decay are often directly 
traceable to one or more of these secondary compounds. Thus we 
always associate the odor of rotten eggs with hydrogen sulphide, 
and the pineapple odor of old, rancid milk with butyric ether. The 
list of known substances which owe their origin to a fermentation 
of this nature is a long one, and in all probability is far from com¬ 
plete. 
The decomposition of urea is of particular interest, since it is 
one of the most fertile sources of ammonia. This transformation 
is brought about by the enzyme urease, which converts urea into 
ammonium carbonate, by simply adding a molecule of water, sim¬ 
ple hydrolysis. Anyone who has been around a stable or a pile of 
fresh manure could not fail to have detected the strong odor of am¬ 
monia liberated from this substance. And right here is where a 
tremendous nitrogen loss occurs. Had the urine, from which the 
ammonia was formed, been absorbed by dry peat, saw dust or a 
