56 KANSAS ACADEMY OF SCIENCE. 
presence of the mineral constituents may have upon the health of the consumers. 
But with the organic matters of a water we have much to do, because these do 
have an influence upon health. 
It is, then, essential that we should know in what ways this organic mat- 
ter appears in a water, what changes it undergoes, what life activities accom- 
pany these, what becomes of it, how its history is recorded, and how all this is 
related to its safe use. It must be said in the outset that even such amounts of 
organic matter as would offend the sight or our sense of smell are not neces- 
sarily injurious to the human system. It is probable that they do affect us by 
weakening our power of resistance when attacked by disease, but we do not know 
as yet in just what way. However, observation and experience have taught us 
that its presence is frequently accompanied by living organisms that seek to 
fasten upon us, to set up disease or cause death. Hence, to the analyst or engi- 
neer who is called upon to judge of the character of a water as to its fitness for 
human use, the mere presence of these organic matters will not lead to a con- 
demnation, but will be regarded as a danger signal which it is wise to heed, even 
to the total rejection of the water when the organic matter indicates conditions 
favorable to the presence of disease germs. 
In making an analysis of water the chemist singles out the nitrogen as the 
significant substance, because this forms so large a part of the objectionable mat- 
ter. In the first stages of the change in vegetable or animal tissue, this appears 
in the form of certain compounds of ammonia which are derived from the organic 
nitrogen of dead matter through the agency of several forms of low plant life— 
the molds, fungi, and certain species of bacteria, which attack it and break it 
up. This isthe process of putrefaction. It may take place in the absence of 
air, and may be accompanied with the evolution of foul odors. When the in- 
soluble organic nitrogen has been thus changed into the soluble forms of albu- 
minoid and free ammonia, these in turn are attacked and broken up into new 
compounds by other species of bacteria, provided that there is present a sufficient 
small amount of oxygen. as this is a necessary element of their life. In the re- 
sult, the nitrogen, as nitrous acid, unites with various bases to form nitrites. 
Then another set of bacteria requiring more oxygen work these over into nitrates, 
a final stage, when the nitrogen has lost its organic character and become com- 
pletely oxidized and mineralized. 
The principal factors in bringing about all these changes are the bacteria, a 
class of very minute microscopic plants, very little known twenty-five years ago, 
but which have been recently studied the world over. We have learned many 
things about them, and have put some of them at work to do our bidding, illus- 
trations of which will be spoken of later. 
But we have not done with the changes that take place in our nitrogen. 
After it has reached the condition of nitrates it is in proper form to become the 
food of plants higher in the scale than those that had used it before. These are 
small, almost microscopic, chlorophyl|-bearing plants, and consequently having 
greenish colors, that float about freely in the water or become attached to larger 
growths. They appropriate the nitrates and restore them again to organic forms 
within their own structure. Then these alge become the food of the lower ani- 
mal life, or, perhaps, die from excess of numbers or lack of sufficient food; when 
the dead matter is attacked anew by the bacteria. This completes the cycle of 
the nitrogen — organic nitrogen, the soluble ammonia compounds, the nitrites, the 
nitrates, and back again to organic state. 
This cycle is not always complete. If the ammonia compounds are set free 
under conditions of little or no oxygen, the nitrifying organisms do not find all 
