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ILLINOIS BIOLOGICAL MONOGRAPHS 



[90 



mental results check very closely with the behavior of the fish in nature; 

 (4) there is a greater tolerance for increased alkalinity than for low alka- 

 linity or acidity; and (5) the experimental data bear out the assumption 

 that the early morning change in the hydrogen-ion concentration of the 

 shore water is sufficient to cause the offshore migration of the species at 

 that time. 



This sensitivity on the part of the silversides suggested an experimental 

 study of the pH of the blood of the species in an effort to ascertain whether 

 or not there is a correlation between the pH preference of the fish and the 

 pH of the body fluid. The procedure followed was that of Levy, Rowntree 

 and Marriott. Celloidin sacs (or dialyzing tubes) were made according to 

 their method, and stored until used in normal salt solution. The idea 

 of the experiment was to obtain an amount of blood of the fish and dialize 

 this blood through the celloidin sac suspended in normal salt solution. 

 The dialysis excludes from the liquid outside of the sac both proteins and 

 coloring matter, but permits the free outflow of hydrogen ions. As the 

 amount of blood obtainable from a single silversides is small — even in the 

 case of the adults — it became necessary to use a number of fish in each 

 experiment. A thin hypodermic needle was inserted directly into the heart 

 of the fish, this being rendered a simple operation by the transparency of 

 the fish. The blood drawn out was placed in a small test tube, the mouth 

 of which was covered with a rubber membrane to exclude the air. In an 

 effort to exclude the maximum amount of air, the test tube was filled with 

 normal salt solution before the rubber membrane was put on, and the 

 liquid was then drawn off by means of a hypodermic needle inserted through 

 the membrane. When 3cc of the blood was obtained, the blood was trans- 

 ferred to the celloidin sac and suspended in a slightly larger glass test tube 

 containing 3cc normal sodium chloride solution. After standing for five 

 minutes, the pH of this solution was read. This experiment was performed 

 on both immature and adult fish with the following results: 



Table 22 

 TESTS OF BLOOD OF YOUNG AND ADULT LA BIDES TEES SICCULUS 



No. Fish used 



Young 

 Av. length 



pH 



No. fish used 



Adults 

 Av. length 



PH 



These results are interesting and instructive, for they show that the pH 

 value of the blood has undergone a modification as the fish mature. It 



