208 VICTOR E. SHELFORD AND W. C. ALLEE 



I. INTRODUCTION 



The importance of atmospheric gases to aquatic animals has 

 been coming more and more to the attention of biologists through 

 the work of Marsh and Gorham ('05), Marsh ('10), and Reuss 

 ('10) on the effect of gases upon fishes; through the studies of 

 reversal of behavior reactions by varying amounts in solution 

 (Loeb '04, Mast '10, Wodsedalek '11, and Allee '12); and through 

 the survey of the distribution of gases, which has been carried 

 on in the Wisconsin lakes by Birge C04, '07a, '07b, '10) and by 

 Birge and Juday ('11). The effect of the different gases, or of 

 varying amounts of a particular gas upon animals has been but 

 little studied. There are many facts concerning the distribution 

 of aquatic animals which do not seem to be explainable on the 

 basis of amount of oxygen considered as a life and death matter 

 fShelford 'lib, and 'lid); the junior author experienced diffi- 

 culty in the control of ^gases in solution in connection with his 

 study of isopod behavior. We accordingly decided to design gas 

 control apparatus and to study the reactions of some group of 

 animals to gas gradients, making it a joint investigation with 

 important bearings upon our separate interests. Fishes were 

 selected because their physiology, habits, and distribution are 

 well known. 



II. ATMOSPHERIC GASES 

 1. OCCURRENCE 



The chief facts concerning the occurrence of gases in nature 

 and their solubility under experimental conditions are shown in 

 table 1. The standard method of expressing quantity of gas 

 in solution is in cubic centimeters per liter at 0°C. and 760 mm. 

 of mercury. All values are therefore given in these terms. 



The amount of each gas that will go into solution from the 

 atmosphere or under experimental conditions, is determined by 

 its solubility and partial pressure and by temperature. The rela- 

 tive solubility of the atmospheric gases is indicated in table 1, 

 by relative amounts going into solution at 20°C. and 760 mm. of 

 mercury. If we desire to increase the total amount of gas in 



