GAS DISEASE IN FISHES. 363 



inipi'oved or corrected b}^ 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 presumabl}' 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 coustautl}" to 

 force the air bul)bles 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 lishes. B}^ appl3dng' devices in the hatcher}", 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, K. H., occurred still another 

 case of a water suppl}" abnormal in its air content, and here an excess 

 of nitrogen coexisted with various degrees of deficiency of 0x3^- 

 gen. The station suppl}" 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 deterniinations of the dissolved 

 ox3"geu and nitrogen in the water of the Nashua station were made 

 and are shown in Table IV, page 374. There appears a deficienc}^ of 

 oxj^gen of greater or less degree and a moderate excess of nitrogen in 

 the water of every source of suppl}" 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 

 l)e 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 quantit};^ 

 of air. The same adjustment occurs with the station water after it has 



