216 
An Unwelcome Truth . 
[April, 
view the case is not very much better. True, a very dilute 
solution of alkaline nitrates will not, so far as is known, 
have any direCtly injurious aCtion upon the health of men 
or animals who may drink it. But should disease germs be 
introduced into the stream — a contingency which can never 
be absolutely excluded — they will find in it abundant pabu- 
lum. Even in the absence of sewage irrigation a stream 
flowing through manured and cultivated lands can never, if 
M. Deherain’s experiments be trustworthy, be absolutely free 
from nitrates. Phosphoric acid will probably be also pre- 
sent, if, at least, wet weather should quickly follow the 
application to the fields adjoining of a manure rich in soluble 
phosphates. This will be especially probable if the soil is 
poor in carbonates of lime or magnesia. From my own 
observations I am inclined to think that if sanitary chemists 
would search more generally and carefully for phosphoric 
acid in the water of streams, ditches, and drains, they would 
be not unfrequently successful. 
I remark here that Dr. B. W. Richardson seems to regard 
the vast quantity of plant-food carried by rivers into the sea 
as a question not of capital moment. He contends that it 
is not lost, but is utilised in the production and maintenance 
of marine organisms. This view is in one sense perfectly 
justifiable. But whatever is withdrawn from immediate 
utilisation is, practically speaking, lost. Were all the plant- 
food thus poured into the sea retained upon the land, it 
might be made to circulate many times through the bodies 
of vegetables and animals in less time than it can be re- 
covered from the sea in the form of fish for human food, or 
fish-manure. For the marine animals which we use for 
either of these purposes do not feed direCtly upon the 
nitrates, the ammonia, and the phosphates which we pour 
into the sea. These bodies serve firstly for the nutrition of 
marine plants, and it is only after a long series of trans- 
formations that they enter the cycle of human wants and 
applications. 
Perhaps the results of M. Deh6rain may help us to un- 
derstand the function of humus. No one, after the many 
experiments and investigations which have been carried out 
will return to the old notion that it furnishes plants with 
any direCt nutriment. But by supplying carbon to the 
oxygen of the air it may retard the oxidising aCtion of the 
latter upon nitrogenous compounds. Its powers of ab- 
sorption and retention also will probably prevent the 
nitrates when actually formed, and the other soluble con- 
stituents of plant-food, from being conveyed away as 
