748 Water in Relation to Health and Disease. 
and farm stock pined and died. All vegetation in the course 
of the stream for some distance was destroyed, as were also the 
fish, and the bottom and sides were thickly covered with a black 
foul-smelling mud and a dark slimy mass of “ sewage fungus.” 
If the pernicious effects of sewage have been most strikingly 
emphasised in connection with ill-conditioned sewage farms, 
they cannot be said to have been restricted to them. Nearly 
every village has its watercourse, and every farm its pond, 
fouled with excremental and other filth, from which farm stock 
obtain their supply ; and if in these instances the effects pro- 
duced are not so deadly, they are nevertheless highly prejudicial 
to animal health. 
In connection with the pollution of streams it is interesting 
to notice that water may be poisonous in one part of a stream 
and not in another, as when sewage contaminated water 
moving from the source of pollution becomes diluted by fresh 
influxes of water from land drains and other sources. In these 
cases the outbreak of disease is localised at a point immediately 
below the intake of the polluting matter. Although the influx 
of sewage or other hurtful matters may continue the same, the 
danger to live stock will vary very considerably from time to 
time. This will depend upon the volume and rapidity of the 
current. In wet seasons, when the former is considerable, the 
offensive matter is carried away by the flood, and becomes much 
less potent for evil than in hot dry weather when water is low, the 
current slow in its movement, and putrefaction is actively going on. 
Further, the course of a stream influences considerably the 
danger arising out of pollution. Where it is winding or tortuous 
the cui’rent becomes slower, and the organic and other matters 
in suspension are allowed to subside and accumulate to a larger 
extent than is permitted in a more direct channel. This settling 
down of the polluting matter would be in some respects an 
advantage, were it not that animals invariably disturb the 
bed of the stream with their feet, and diffuse the sediment 
through the water each time they drink. It is this habit of 
entering the stream or pond, with its disturbing influence, which 
aggravates the dangers of pollution to live stock. 
Where water has been affirmed to be the cause of disease 
it has frequently been urged, to the contrary, that the sickness 
was confined to particular periods, or particular parts of the 
stream, while the water had been in constant use by large 
numbers of animals in the whole tract of the watercourse, and 
had nowhere else shown hurtful properties. To such objections 
as these the above considerations appear to furnish a sufficient 
explanation. 
