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THE AMERICAN NATURALIST [Vol. XLII 



demands that fishes shall be kept under observation, in a 

 healthy condition, for days or weeks. Some method of 

 treatment was deemed advisable which should be ap- 

 plicable to the water supply as a whole. Thus far, no 

 attempts to prevent the entrance of air into the pump, 

 along with the water, have been permanently successful. 

 The wooden suction-pipe, through which the pump 

 formerly received its supply of sea-water, was replaced, 

 early in 1903, by a metal one, the assumption being made 

 that the pofous condition of the former was responsible 

 for the trouble. Indeed, Marsh and Gorham, writing 

 during the following year, declare that "the replacement 

 of the old suction pipe with a new impervious one 

 abolished all signs of the gas disease at Woods Hole." 

 But the malady was again rife during the summer of 

 1905, and has given much trouble during the seasons of 

 1906 and 1907. In the absence of definite information as 

 to the present source of the air in the water, the most 

 promising mode of attacking the difficulty seemed to be 

 the construction, on a large scale, of a deaerator, which 

 should operate on the same principle as the pans and 

 boards before employed for individual aquaria. Accord- 

 ingly a series of five wooden trays was built, these lying 

 in a zig-zag series, one above the other, and having a 

 total bottom area of about 10,000 square inches, thus 

 bringing a large surface of water into contact with the 

 air. Perhaps the most effective factor in the case, how- 

 ever, is the splashing of the water in its descent from one 

 trough to the other and from the lowermost of these into 

 the supply tank below. From the latter the water is 

 distributed to the laboratory. 



This deaeration apparatus was not constructed until 

 late in the past laboratory season, but the results of the 

 tests already made seem well worth recording. The fatal 

 effects of the water from the local supply had been con- 

 spicuous throughout the summer. It may be mentioned, 

 by way of example, that in one wooden tank in the hatch- 

 ing room twenty tautog died in a single day, apparently 



