Tue MicroscoricaL News 
AND 
NORTHERN MICROSCOPIST. 
No. 46. OCTOBER. 1884. 
ON THE DETECTION OF SEWAGE CONTAMINA- 
TION BY THE USE OF THE MICROSCOERE 
AND -ON THE PURIFYING. ACTION OF 
MINUTE ANIMALS AND PLANTS. 
By HL Cy Sorpy, LED, F:RS; 
Y studying with the microscope the solid matters deposited 
from the water of a river, the previous contamination with 
sewage can usually be detected without any considerable difficulty. 
If the amount be serious, the characteristic particles of human 
excrement can easily be seen; and even if it is small, and has been 
carried a long way by the current, it can usually be recognised by 
means of the hairs of oats derived mainly from the droppings of 
horses, which resist decomposition for a long time, and are not 
consumed as food by minute animals. I, however, do not propose 
to enter into detail in connection with this part of my subject, but 
specially desire to call attention to the connection between the 
number of minute animals and plants, and the character of the 
water in which they live, and also to their influence in removing 
organic impurities. 
For some time past I have been carefully ascertaining the 
number per gallon in different samples of river and sea water, of 
the various small animals which are large enough not to pass 
through a sieve, the meshes of which are about 335 part of an 
inch in diameter. The amount of water used varies from ten 
gallons downwards, according to the number present. By the 
arrangements used there is no important difficulty in carrying out 
the whole method in a satisfactory manner. I confine my remarks 
entirely to general mean results. 
The chief animals met with in fresh water are various entomos- 
traca, rotifera, and the worm-like larve of insects. I find that the 
number per gallon and per-centage relationship of these mark, in 
VOL. IV. 
