How to obtain it. 203 
as well as friends to encounter, and by cultivating haphazard all 
the aquatic creatures that we come across, we may be doing harm 
instead of good. There are probably few of the minute organisms 
which we meet with which are not devoured with avidity by large 
trout, but there are many which, if introduced into a fry pond, 
would soon reduce the stock of fish contained therein considerably. 
This is one cause by which trout sometimes seem to die 
unaccountably in the fry stage. I have seen, years ago, thousands 
of little fish dropping down dead for no apparent 
reason. It has since been ascertained that these had 
probably been attacked by parasites. 
There are myriads of small creatures, which are 
highly useful as food for fry, known as infusoria. 
Some of the best known among these are probably 
the Rotifera (commonly known as rotifers or wheel- 
insects), but they are very minute, and as far as our 
Fig. 22, present knowledge has attained cannot be cultivated 
Rotifer, enl® on a commercial scale. 
The secret of the successful cultivation of most, and probably 
all the minute forms of life, lies largely in the protection of them 
from their natural enemies. The same lines have to be followed 
as in the case of large game. We must provide for them safe 
undisturbed breeding grounds, and suitable food. We often find 
that Nature works out these deeply interesting matters with 
unerring exactitude, making due provision for everything. Nothing 
is overlooked. Now, it does not suit Nature’s purpose to have 
great crowds of any individual creature in one place, except in a 
few exceptional cases, and hence there are many causes which 
tend to keep in check the superabundance of life, which would 
otherwise be found existing. The same applies to the fish. We 
do not find a pool in the natural stream, as a rule, abounding in 
fine large trout. We know that this is the exception; but we 
also know that it can be brought about by artificial means. 
So, then, with the more minute forms of life. If we apply the 
same rules that attach to the cultivation of the fish, we obtain the 
same result, viz, an enormous multiplication of individuals. 
Whilst multiplying the fish on the one hand, we must multiply the 
creatures on which the fish feed on the other,.and so the two 
