no Pub. Puget Sound Biol. Sta. Vol. 2, No. 39 



PLATE 19 



Fig, 1 show the arrangement of glassware by which running- 

 water mixtures of sea-water, acids, etc., were obtained. A is the dropping 

 chamber, made up of the bulb of a 50 cc. pipette with a piece of tubing 

 drawn to a dropping point, in this case the lower half of a broken 1 cc. 

 pipette, projecting into it from above. The dropping tube was connected 

 with a supply bottle of acid or other chemical and the number of drops 

 regulated with a screw pinch-cock. The dropping chamber should be two 

 or three feet above the mixing bottle (B) ; it is shown closer here merely 

 for convenience in drawing. The mixing bottle (B) held only about 

 200 cc, so as to make changes of flow easy. The water entered through 

 the left tube, which extends to the bottom very close to the one from the 

 dropping chamber. The mixture left the bottle through the right tube 

 ending at the lower level of the cork. C shows the 100 cc. cylinder into 

 which the flow could be turned for taking samples by means of pinch-cocks. 

 Z) is the experimental bottle, holding two to three liters; it is the one 

 into which the fish were introduced. 



Fig. 2 shows a cheap form of gradient tank which was found very 

 effective. Water was introduced into the two ends through tees as shown 

 below the inlet pipes (i). It flowed out at the center from both top and 

 bottom, through a hole on each side. Instead of some of the elaborate 

 arrangement of pipes described elsewhere, the tubes leading from the 

 openings projected only a little outside of the tank; rubber tubes were 

 attached to these and brought from the bottom openings to one side and 

 from the top openings to one end where they were joined with glass 

 Y's (o and o'). The outflow was adjusted by means of pinch-cocks so 

 that the same amount came from each side, and the same total from the 

 top and from the bottom. The front was of glass, in two panes. The 

 tank was approximately 120 cm. long, IS cm. wide and 15 cm. deep. 



Fig. 3 shows a longitudinal section of the gradient tank. The M 

 end is the modified water end shown by black lines; the P end is the 

 polluted water end. There is a suggestion of a gradient between the two 

 kinds of water in the center third. The thirds are indicated by the short 

 vertical lines below. 



