WATER, AND ITS IMPURITIES. 159 
one generation of plants affords the food requisite for the growth 
and sustenance of a second. 
But certain inorganic substances also favour greatly the 
growth of plants, as the phosphates and ammonia ; the latter, 
probably, on account of the nitrogen it contains ; and hence the 
value of animal manures, which contain these compounds largely, 
in promoting the growth of vegetation. 
Again, analysis has shewn that every animal contains pre- 
cisely the same elements as the vegetable ; with this important 
difference, however, that the proportion of nitrogen is much 
greater in the former. 
It thus appears that, while vegetable substances in a state of 
decay are best adapted to the maintenance of vegetation, animal 
matter, in a similar state, is the best suited to sustain a large 
amount of animal life. 
These particulars are capable of important practical appli- 
cation, inasmuch as they declare to us that every water which 
abounds in living animal forms, especially infusoria, must also 
contain dead animal matter in abundance. 
The true interpretation to be placed on the presence of in- 
fusoria in water was not well understood until Dr. Hassall called 
particular attention to the condition of animalcular life in Thames 
water near to London. 
The relation of dead to living organic matter is well shewn by 
simply diffusing a little albumen through a wine-glass of dis- 
tilled water : in a few days, and especially if the weather be 
warm, the infusion will be found literally to swarm with ani- 
malculae. 
But there are some other circumstances, independent of the 
amount of dead organic matter contained in water, which 
determine the kind of living productions present in it. 
One of these, and a very important one, is the condition of 
the water as to alkalinity or acidity. If the water have a decided 
acid re-action, and contain a large amount of animal matter in so- 
lution, there will be an abundant development of fungi in the 
course of a few days; but if, on the other hand, it exhibits an 
alkaline re-action, then, instead of fungi, animalculae will be 
developed. 
These curious and important facts may be readily shewn by 
experiment. Let two solutions of albumen in water be pre- 
pared, the one being rendered alkaline, the other acid ; in the 
first, in the course of a short time, infusoria will appear, while 
in the second, in an equally short period, a scum of fungi will 
become visible to the naked eye. 
Now fungi are usually regarded by the naturalist as vege- 
table productions, having, however, a resemblance to animals 
