REPORT OF COMMISSIONER OF FISH AND FISHERIES. 95 
found that eggs, representative of the shad and whitefish, could be 
closely imitated in roundness, size, and transparency. Those intended 
to represent smaller eggs, as of the Spanish mackerel and codfish, were 
produced by pouring melted resin through sieves from an elevation, the 
falling particles being caught in water. The latter class had to be 
screened to separate the different sizes, those made by means of tubes 
being practically uniform. During some months attention was paid 
almost wholly to the selection of substances which could be united to 
produce a composition of required specific gravity for eggs semi-buoyant 
and floating. Meantime the point of obtaining eggs of perfect roand- 
ness was solved, and while yet looking to the regulation of the specific 
eravity it was accidentally found that eggs of resin could be made to 
represent any desired specific gravity by subjecting them to solutions 
of salt water of relative densities. When this was ascertained it was 
readily seen that both kinds were possible from the same material, the 
brine for the semi-buoyant ones requiring to be weaker and for the 
floating ones stronger. 
Another duty devolving upon the superintendent was that of assist- 
ing the Commissioner in preparing for and carrying out experiments 
for determining the relative value of artificial salt water as the basis 
of maintaining an exhibit of marine animals and plants at the Colum- 
bian Exposition. As it was impracticable to devise satisfactory means — 
for circulating the small quantity of water with which he was experi- 
menting, it was necessary to adopt the alternative of oxygenizing the 
water by means of air circulation. As long ago as October, 1888, while 
the Ohio Valley Exposition at Cincinnati was occupying attention, 
instructions were received from the Commissioner to establish a small 
number of aquaria in the west end of the building and provide therefor 
an air circulation. Attempts were then made to liberate air through 
rubber tubing gashed with a knife or perforated with pin holes, but 
without good results. Following this, tests were made with sections 
of grapevine and other twigs selected from the mass of driftwood found 
on the shores of the Potomac at the shad-egg station. Grapevine 
gave tolerably fair results, but in time it was discarded, and Mr. W. P. 
Seal, then in charge of the aquaria, adopted sponge, a crude alternative, 
which, being cut into small pieces, was thrust into holes punched into 
half-inch rubber tubing. 
All former efforts to diffuse volumes of air through water in currents 
sufficiently minute to effect ideal aération having failed, and the solu- 
tion of the problem being dependent upon the application of air circu- 
lation, active steps were taken to discover a material of the desired 
porosity. Plugs were made in cross-section from various kinds of wood, 
with the hope of finding one of suitable porosity. Mr. L. G. Harron 
removed a dead branch from an American linden tree on the public 
Mall, and it was just what was desired. From that day the question of 
successful liberation of air in water, for our purposes, has been solved. 
