150 JOHN N. LOWE 



I wish, here, to express my chief indebtedness to Prof. 

 M. F. Guyer, for his kindly criticism and suggestions during the 

 progress of the work. To Prof. A. S. Loevenhart, I wish to 

 acknowledge my appreciation of many courtesies extended. For 

 the privilege and use of the fish hatchery and trout embryos, I 

 desire to express my appreciation of the favor to Dean E. A. 

 Birge and Superintendent James Nevin of the Wisconsin Fish 

 Commission. 



Reactions to gases 



1 . Oxygen. The oxygen used in these experiments was chemi- 

 cally pure. The pigment cells remained expanded in an atmos- 

 phere of oxygen, and the fish hved indefinitely. 



The hydrogen used in these experiments was obtained by the 

 action of chemically pure hydrochloric acid on Merck's highest 

 purity zinc. The gas was passed through two towers of KOH 

 and then through two towers of distilled water, of which one 

 had red litmus, and the other blue litmus. The trout were in 

 the fifth tower. 



The pigment cells contracted completely in four to six min- 

 utes when the embryos were exposed to hydrogen. If oxygen 

 was substituted before the fish died the pigment cells expanded. 

 If the oxygen was again replaced by hydrogen the pigment cells 

 contracted. The results of these experiments* show (1) that the 

 absence of oxygen caused a contraction of the melanophores; 

 (2) that the oxygen is necessary for the maintenance of the 

 expanded pigment cells. 



2. Carbon dioxide. The carbon dioxide was generated through 

 the interaction of chemically pure hydrochloric acid on marble. 

 The gas was purified by being passed through a tower of sodium 

 bicarbonate and then through a tower of acidified lead acetate, 

 and lastly through two towers of distilled water. 



The fish were exposed to water through which the carbon di- 

 oxide was bubbling in a steady slow stream. The carbon dioxide 

 produced a complete contraction of the pigment in two and one- 

 half minutes. The time of contraction was the same for all the 



