72 THE CIECULATION OF NITEOGEN IN NATUEE. 
might render the nitrification imperfect, and a well-water that 
showed nitrates to-day might contain organic matter to-mor- 
row merely in consequence [of a heavy rainfall, and that this 
constitnted a real danger. Modern bacteriological research 
has shown that even this was far too favourable a view to 
take of such water. Nitrification is essentially an oxidation 
it is true, but that is not synonymous with the destructive 
process implied in the expression " burnt up." It is a 
biological oxidation .exerted upon the dead and comparatively 
innocent organic matters ; it does not in any way affect the 
specific germs oi disease which may be present in the 
original sewage. Precisely similar phenomena are observed 
in all fermentative processes, such for instance as brewing. 
Whilst the yeast is in full activity breaking up the dead 
organic matters of the wort, other micro-organisms which 
may have accompanied it merely bide their time, and when 
the conditions become favourable spring into activity, and 
unless suitable precautions are taken the beer may become 
acid, or ropy, or putrid, or even become entirely converted 
into vinegar. 
In precisely the same way the typhoid or cholera 
organisms are indifferent to the action of the nitrifying 
microbes, and quietly await their entry into their favourable 
habitat — the digestive system of man. Whilst sewage was 
being completely nitrified in the filter before you, a culture 
of cholera germs was passed through, and the filtrate 
contained numerous vigorous spirilla for many hours. Of 
course, after a certain amount of percolation the water will 
become freed from bacteria ; but by that time, as I have 
shown, the nitrates also will have ceased to exist. It must 
be admitted, therefore, that drinking nitrified sewage either 
neat or diluted with pure water is a dangerous as well as 
nasty practice. \ <dv:,j:, j id: ■ 
