GAS DISEASE IN FISHES. 3638 
improved or corrected by exposure to the air, and these controls 
suffered no loss. 
Determinations of the degree of excess of nitrogen in the Erwin 
water have not been made on freshly taken samples. The origin of 
the excess is to be looked for in the rising gas and the necessary pres- 
sure factor in the weight of the column of springing water. The air 
bubbles are presumably mingled with this water for a distance below 
the restricted areas of emergence in the spring in its subterranean 
course and even the whole distance back to its surface origin. The 
greatest depth reached by the water beneath the spring is unknown, 
but is estimated from the geology of the region to be at least 100 feet, 
and may be several hundred. ‘This depth represents the height of the 
column of water, the pressure of which is operating constantly to 
force the air bubbles into solution. The supply of bubbles is abun- 
dant and never failing, and the water is bound to take up more air 
than it can hold when it reaches the surface and becomes exposed to 
the atmosphere at atmospheric pressure only. Here the excess begins 
to escape; and as the spring is shallow and well exposed, this process 
is rapid; yet the constant flow keeps the body of water constantly 
supersaturated.. In flowing away from the spring in shallow exposed 
channels the water soon corrects itself, becoming normal and harmless 
to fishes. By applying devices in the hatehery, thoroughly exposing 
to the air the water supplying the troughs, the gas symptoms disap- 
peared and the losses were reduced to the normal for all fish-cultural 
operations. 
CONDITIONS AT NASHUA, N. H. 
At the fisheries station at Nashua, N. H., occurred still another 
case of a water supply abnormal in its air content, and here an excess 
of nitrogen coexisted with various degrees of deficiency of oxy- 
gen. The station supply came largely from rather shallow artesian 
wells, some of which entered the hatchery directly, while others were 
driven in the bottom of the nursery and rearing ponds and on the edge 
of the larger brood ponds. Many field determinations of the dissolved 
oxygen and nitrogen in the water of the Nashua station were made 
and are shown in Table IV, page 374. There appears a deficiency of 
oxygen of greater or less degree and a moderate excess of nitrogen in 
the water of every source of supply save that from the taps of the 
Nashua city service. This latter water, however, at its source in arte- 
sian wells (Pennichuck wells) is even more abnormal as to dissolved 
air than is the station water, the oxygen being less, the nitrogen about 
the same. While not insanitary for city purposes, it would doubtless 
be fatal to fishes. The aeration and deaeration it receives in the open 
stream which takes it to the reservoir adjust these abnormalities, so 
that as delivered from the service pipes it has about a normal quantity 
of air. The same adjustment occurs with the station water after it has 
