162 Flow to obtain it. 
Take care to keep everything very clean, therefore; keep the 
boxes covered, and have all the woodwork well varnished, and 
there is little to fear from this enemy. 
Sediment is also a danger which should be carefully guarded 
against. Unless great care be taken it is sure to come, and to 
settle more, or less upon the ova. Although I have known cases 
in which sediment has apparently had no very prejudicial effect 
upon ova, yet other cases have come under my notice in which 
very serious harm has accrued. At some periods of their existence 
eggs would not be so much affected by it as at others, and the 
sediment itself varies very much according to circumstances. In 
some waters it would be almost entirely mineral, whilst in others 
it would be chiefly of a vegetable or organic nature. Or it might 
consist of both mineral and vegetable matter. Some deposits are 
directly poisonous, as for instance in cases where copper or lead 
are present. Others again are highly injurious, as for instance 
iron or lime, although I have seen good work done in water 
containing both. But assuming that a sediment could deposit on 
the eggs, of such a nature as to be quite innocuous in itself, the 
result must tend towards suffocation. This may be only partial, 
but, nevertheless, it is sufficient to arrest the development of the 
embryo, and as a consequence deformities are produced. It is 
well known that the ova of salmonoids require a good supply of 
oxygen. They likewise give off carbon, which requires to be 
carried away from the eggs as produced, and when covered with 
sediment this healthy change of condition is not maintained, and 
should it remain long enough many of the eggs will be poisoned. 
Although they may not be absolutely killed at the time, the result 
will probably be weakly or deformed fish. 
When eggs are packed in moss and sent long distances 
cripples usually occur in excess amongst the fry produced. This 
has been notably the case amongst eggs imported from abroad. 
It is not at all surprising that this should be so when the develop- 
ment of the embryo is considered. The pressure, slight as it may 
be, of the layers of moss upon the eggs, is quite enough to cause 
the many curved spines and other deformities, that occur under 
such conditions. Concussion has also been found to produce a 
similar effect, and often to cause the death of the embryo. 
