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MICROSCOPIC EXAMINATION OF WATER. 
worms. On a grass surface, the rain carries off a great deal of 
matter which could never be reached but for the action of 
the earth-worm; so that while the grass protects the surface 
to some extent, the earth-worm neutralises this protective 
effect, and enables the rain to be constantly washing particles 
of soil from off the surface. The vegetable soil which is 
often found to have accumulated in hollows, almost entirely 
results from this. Apparently, nothing could be so perma¬ 
nent as a grass-covered surface; yet it is being continually 
raised by worms, plants, &c., and lowered by the washing 
effects of the rain. Indeed, any soil, if it is to continue fer¬ 
tile, must be constantly changing, for on the process of decay 
and renewal fertility depends.—J. H. 
THE MICROSCOPIC EXAMINATION OE WATER. 
The chemical examination of water leaves, as is well 
known, much to be desired from a sanitary point of view. 
It informs us of the condition with which organisms may be 
associated, but gives no information as to the presence of 
organisms. The microscope, as at present used, reveals only 
the coarser forms of animal life, and those only with uncer¬ 
tainty. M. Certes has endeavoured to ascertain how far it 
can be made to yield information of more direct value. The 
discovery of the microscopic organisms has hitherto been 
very much a matter of chance. Patience and skill are even 
of slight help. Fortunately, however, certain chemical re¬ 
agents kill these organisms without changing their appear¬ 
ance; osmic acid is of especial value for this purpose. Once 
destroyed, they sink to the bottom, and, if enough of the 
liquid has been employed, they may thus be collected in 
appreciable quantity. The value of this method is shown 
by the following experiment:—If a test tube be broken, and 
the water it contained is contaminated by dipping in it the 
extremity of a rod which has been placed in an infusorial 
liquid, and it is then treated with osmic acid, the organisms 
will be found intact, and with readiness, by the aid of the 
microscope. 
In the examination of water M. Certes employs a one and 
a half per cent, solution of osmic acid. One cubic centi¬ 
metre of this solution will suffice for thirty or forty cubic 
centimetres of water, all animal and vegetable organisms 
being by it rapidly killed and fixed. In a few minutes, in 
order to lessen the blackening action of the osmic acid, as 
much pure water as the test tube will hold is added. In 
