58 KANSAS ACADEMY OF SCIENCE. 
the life of those which are our enemies. But this relationship has not yet been 
worked out. Then, too, there are no practical tests that can be applied to a 
water by which the presence of these dangerous germs may with certainty be de- 
tected. Perhaps no such tests will ever be found, because of the comparative 
small number of the enemy that may find their way into the water, and the con- 
sequent small probability of catching some of them in taking any sample for ex- 
amination. Probably we shall have to remain content with indirect methods, 
from which the presence of these germs may be inferred, rather than to expect 
the development of any method for their direct detection. 
Something more must be said regarding the alge. Investigators of low water 
life have been so attracted by the infinitesimal bacteria that these plants have 
been much neglected. Inasmuch as a once-polluted water cannot be said to be 
wholly purified until its nitrogen has gone through a complete cycle, until its 
nitrates have been used by the algz and these have disappeared through starva- 
tion, it seems probable that a knowledge of their habits would enable us to use 
some of them in correcting bad conditions produced by other forms of life, and, 
on the other hand, to prevent the appearance of evils that sometimes arise in con- 
nection with an excessive growth of some species of these plants themselves. 
Mrs. Richards, in her recent book, ‘‘ Air, Water, and Food,”’ hastthis to say 
concerning these plants: 
‘*Tt is organisms of this class which give tastes and odors to water, and which, 
if enough were known concerning them, would probably give perfectly trust- 
worthy information as to the past history or source of contamination. The two 
classes of organisms work in opposite directions, and, so long as food is present 
for either, life will increase with proportional rapidity. When a ground-water, 
free from all organic matter, but rich in nitrates, is exposed in an open basin, the 
rich growth of chlorophyll-bearing alge follows as a matter of course; later, 
decay sets in and products of decomposition abound, the air above being the 
source of a constant supply of spores of all kinds. 
‘*When a house or barn drain empties into a small, sluggish stream, it soon 
becomes filled with green plants thriving on the ammonia, and it is often pos- 
sible to trace the source of pollution of a large lake by the line of green amcebina 
leading to the insignificant ditch. 
‘*The effect of storage of water containing high nitrates in open tanks or res- 
ervoirs exposed to the collection of dust will be that spores of chlorophyll-bearing 
alge, diatoms, desmids, etc., will soon develop, and will increase as long as the 
mineral] food lasts. Only by protection from dust and light can such water be 
kept free from unpleasant accumulations of suspended organisms or from disa- 
greeable tastes. Unpolluted surface-waters, on the other hand, improve on stor- 
age, as a general rule, if the basin is a clean one. The storage of polluted or 
clarified water is thus forbidden, since not infrequently the first indication of the 
pollution of a surface supply is given by the appearance of some member of that 
richly nitrogenous group of alge called Cyanophycex, or ‘blue greens,’ from the 
presence of blue or purple coloring matter along with the yellow-green chloro- 
phyll. Since this group of plants contains from seven to eleven per cent. of ni- 
trogen, while other groups contain only one or two, it is evident that, if it is to 
flourish, more nitrogenous food must be supplied. This may be derived from 
fertilized fields, from decay of other vegetable life, as well as from the richer 
source of direct sewage; but, in any case, the growth of these plants is a sign of 
abundant food supply, which must be cut off if they are to be starved out, as 
they must be, unless they are removed while fresh by straining or skimming, for 
the odor of their decay is so intolerable as to preclude the use of the water. In 
