Water in Relation to Wealth and Disease. 
737 
We cannot draw general conclusions from individual cases, 
but when we find, as we have done, nine or ten dairy cows 
suffering from tubercular disease in the course of a year on a 
farm irrigated with sewage, the idea of sewage as a possible 
cause of the malady may be reasonably entertained as a starting- 
point for further inquir}-. It would be perfectly true to say that 
grass grown under the influence of sewage may be, and is, fed to 
cows for long periods without occasioning impairment of health ; 
but it is quite another thing to aver that human sewage has no 
ill effects on cattle. 
Acute sewage poisoning sometimes proves rapidly fatal, and 
we have known cattle to die from its effects in a few hours. 
Where it assumes a chronic form, the disease runs a slow 
and protracted course, extending over weeks and months. In the 
former case, the malady develops many of the clinical characters 
of anthrax ; in the latter it is marked by a continuous diarrhoea, 
often resulting in emaciation and fatal exhaustion. 
It will be seen from what has been said of the disposition of 
water that, while in nature there is a constant tendency to con- 
tamination, there is also a never-ceasing process of cleansing 
going on, whereby it is purged more or less completely of its 
organic filth, and again fitted for consumption. Natural purifi- 
cation not only takes place in that portion of the water which 
enters the soil, but in that other moiety also which passes 
more directly from the surface into our ponds and rivers. 
The influence of animal and vegetable life on the purity of 
the latter is very considerable, but has hitherto received little 
attention. It may, however, be safely affirmed of it that 
much of the organic matter poured into, and produced in, 
our watercourses is consumed by birds, fish, and other living 
creatures, who feed upon it ; and there can be no doubt that 
some forms of vegetation which abound in our rivers, ponds, 
and brooks also exercise a salutary influence on the medium in 
which they grow. It is not, perhaps, less true that certain low 
forms of plant life tend rather to vitiate than to purify, whilst 
others serve as an index of foulness and filth. In a short 
but interesting paper by Mr. A. W. Bennett on “ Vegetable 
Growths as Evidence of the Purity and Impurity of Water ” the 
vegetation of running streams is classified under four heads. 
These comprise — 
Action of Animals and Plants. 
1. Flowering Plants. 
2. Fungi. 
3. Algae, 
4. Characeae. 
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