13 
in my judgment, when the state should consider seriously the policy 
of preserving adequate breeding grounds and feeding grounds for 
our river fishes, even if it has to acquire and maintain them, since 
these waters are in imminent danger otherwise of being practically 
depopulated. 
It is another interesting conclusion from our recent work that 
the enormous outpouring of Chicago sewage into the upper Illinois 
improves rather than impairs its fitness for the maintenance 
of fishes. The organic wastes thus emptied into the stream are laid 
hold of by bacteria and Protozoa, and passed up by successive steps 
to form the flesh and bones of fishes, and thus finally those of men. 
The same may be said of the organic wastes of the towns along the 
banks of the stream. 
Still another conclusion of considerable practical interest may be 
here mentioned, although it grew out of our aquatic work outside 
the Illinois basin. One large section of the state of Illinois, com¬ 
prising about a fifth of its area, is peculiar in the absence, or at 
least in the unusual rarity there, of a considerable group of fishes 
which are abundant elsewhere in the state and elsewhere in the sur¬ 
rounding territory. Now this section, the conditions of which these 
fishes evidently do not tolerate, is distinguished from the remainder 
of the state by its geological history, and, as a consequence, by the 
different character of its soil and of its streams. The soil is so 
finely divided that its particles can not be wholly separated from the 
water, even by repeated filtering with the finest filter papers, and 
it thus remains persistently and perpetually turbid. The fishes which 
seem to avoid this situation are, on the whole, those which we find 
in other parts of the state to be relatively infrequent in very muddy 
water. The inference is plain that it is the permanently muddy char¬ 
acter of these southern Illinois streams, itself due to the geograph¬ 
ical history of the district, which renders them unfit for these more 
sensitive fishes. Any attempt, consequently, to increase the number 
of such fishes there would be foredoomed to failure. Doubtless 
there are many other instances of the same sort to be found in 
other parts of the country, and it seems possible that various mys¬ 
terious failures of attempts made to introduce new fishes are at¬ 
tributable to some such cause, not taken into account because un¬ 
known. 
We have now a long- waiting list of special practical inquiries 
which seem clamoring to be made. We need, for example, to ob¬ 
serve most carefully the European carp, now undergoing enormous 
multiplication in our interior waters; to learn the details and the 
