308 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
remains nearly clear, it is somewliat easy to catch the animals, and one may so become convinced of 
the phenomenal increase. 
Under the influence of water and warmth a vast develoijment takes place of those numerous 
microorganisms contained in the cow manure which absorb the iTiidigested parts of the manure, and 
which serve themselves as food for the Crustacea. The manure gradually disappeared during the 
months of May, June, and July. When these Crustacea are fed to small carjt or goldfishes a gradual 
transformation of cow dung into fish is accomplished, almost without the help of plants. 
The Qammariis pulex has lately frequently been found in large quantities between old bricks and 
half-rotten brush wood in the Endenich Brook, near Bonn, without any cells containing chlorophyl 
having been found in the water or mud. The water of the brook was muddy, because it contained the 
waste and drainage of several adjoining villages. This relatively large crustacean grows splendidly 
in an aquarium i^repared with cow dung, as previously described, if a little dry brush wood is added. 
Practically, it will be easy to produce this transformation of cow dung into fish, subject to local 
conditions. The most advantageous way would seem to be to dig ditches along the banks of the pond 
about 1 meter wide and 25 centimeters deep (about 40 inches by 10 inches) connected with the pond 
by numerous narrow cuts. Perforated boxes or flower x>ots filled with cow dung are then placed in 
these ditches and protected from the rays of the sun. When this shallow water is warmed by the sun 
a great quantity of infusoria and Crustacea will develop, which by the rise and fall of the water in 
the pond are sucked into it. If the banks of the pond are low, the fertilizing substance will settle 
there, thus enlarging the area for the breeding of the Crustacea and forming a feeding-place for the 
young fishes. 
All these infusoria are especially sensitive to light. The ditches and banks must have old bricks, 
brushwood, leaves, etc., for the protection of animal life. A luxuriant growth of water plants, 
esiiecially TVolffia, must be prevented, because it absorbs too much nourishment from the water; that 
is, the nourishment is collected in the plant in such a shape that it is unserviceable for the purposes 
of fish proimgatiou.* 
These breeding ditches must, if possible, be dry in winter, so that the frost may easily penetrate. 
In that case the winter eggs of the Crustacea, bedded in the mire, will develoii better and more numer- 
ously in the spring than when having overwintered in water. It would be very interesting, but very 
difficult, to determine the causes of this iieculiar process. Dr. Kochs exposed the mud of several 
aquaria in an open box to the sun, to raiu, and to frost by keeping it in the gutter of the roof of his 
residence. By putting samples in glass vessels filled with boiled hjulrant water and j)lacing them in 
a warm room, there developed within three weeks Cypris, Daplmia, and microscopic wheel animalculfe, 
especially JTi/drtbna sea /« aud infusoria. It is certain that the eggs had several times been exposed 
to — C. (14° F.). At the end of May several samples of the same, now air-dried mud, were put into 
water previously boiled, and in two weeks numerous Crustacea had again developed. By drying a 
large quantity of egg-containing mud in the fall, the proper food may easily l)e bred in the sirring and 
summer. 
It must here be stated that the eggs will not stand a drying over sulphuric or anhydric phosphoric 
acid. When that is done they all die, as has often been observed. This is mentioned because it is 
frequently asserted that theeggsof the lower animals may live for one or more years in the thoroughly 
dried mud puddles. Even mud, cleft and disrupted by the action of the sun, still contains several 
parts of water. A total drying up of the eggs, therefore, does not take place in nature. 
Dr. Kochs made special experiments with the Helix pomatia, and found that under the usual condi- 
tions the moisture of the living animal does not dry up in a year, even in a warm room ; moreover, as 
soon as a dry crust has been formed around it, it loses the moisture only in artificially dried air, but 
it dies before all the moisture is absorbed. The poisonous substances forming at the bottom of the 
lionds by a slow decomposition of organic substances at such times of the year when there is no frost 
are destroyed by the plant life. These infusoria, and also the eggs of the lower animals, are frequently 
threatened by an accumulation of those poisonous substances during such times in winter when this 
process does not take place. Half-decomposed organic substances are loosened and made spongy by 
the frost, and later on easilj^ crumble or dissolve. Only the drying and freezing of the mud, there- 
fore, can be recommended. 
* I think it pertinent at this point to remark that Dr. Kochs’s warning against allowing a luxuriant 
growth of water plants in the ponds has reference to his method of “ transforming cow dung into fish 
without the help of plants.” Ordinarily — that is to say, naturally — the vis or fertilizing strength of the 
manure would go to making a luxuriant growth of plant life, which in turn would be converted into 
the low forms of animal life exhibited in the infusoria and Crustacea. 
