198 Tliirly-Secoiid A-niiual Meeting 



original cause and of the mechanical process which usually is 

 the immediate occasion of death. Leaks in a pipe were at tha 

 bottom of the whole trouble, and the leaks introduced nothing 

 more remarkable than air. Parasites, bacterial or otherwise, are 

 not concerned; but purely physical causes alone, the laws of 

 which have long been known. Thirdly, the essential and active 

 agent, air, which alone is the immediate cause of- death, is one 

 whose lesser constituent, oxygen, is absolutely necessary to the 

 life of fishes and of most living things. The mortality is a con- 

 spicuous example of too much of a good thing. Without enter- 

 ing into, partly from ignorance, the separate roles played by the 

 oxygen and nitrogen of the air in respiration in fishes, it may be 

 remarked that the respiratory mechanism is nicely adjusted to 

 water containing air the amount of which is within certain 

 limits, — on the one hand enough to barely oxidize the blood, on 

 the other to the point of saturation. Below oue limit and suffo- 

 cation results ; aljove the other limit and, strangely enough, suffo- 

 cation may result also, but more indirectly, first mechanically 

 stopping the circulation. Between these limits all fish cultural 

 operations, with adults at least, whether of nature or by artifice, 

 must be carried on. 



It must not be supposed that nature always avoids surpass- 

 ing either of these limits. It is well known that springs are 

 apt to deliver water lacking in air, — not well aerated. On the 

 other hand, wherever it is possible for air to accompany spring 

 waters through any part of their course, it will pass into solution 

 according to the depth at which their air is present. This may 

 of course 1)e considerable and some springs do give forth water 

 containing an actual excess of dissolved air. The degree of ex- 

 cess is doul)tless much less than tliat of the Woods Hole water. 

 In these cases air will usually be seen to bubble intermittently 

 from the spring bottom. As the water flows away from such a 

 spring, the excess passes off and the water soon corrects itself. 



'I'he Woods Hole occurrence' impresses upon fish culturists 

 nnd managers of large aquaria the fact that where pumps supply 

 the head foi- tlie gravity system, a danger constantly menaces. It 

 may remain in al)eyance and never do any damage. If the suc- 

 tion ])i]ie is intact — quite ini]X'r\ious — wliere it is not under 

 Wiitci', and no free air can l)e taken u]i with tlie water at the point 



