RESISTANCE OF FISHES TO LACK OF OXYGEN. 451 



will be remembered (Fig. i) that the normal resistance of the 

 rock bass rises rapidly during the fall and winter months. We 

 are at the same time accustomed to thinking of the breeding 

 season in most animals as being a period of high metabolic 

 activity and there is much evidence for this belief. It is, how- 

 ever, at the beginning of the breeding period that we find the 

 fishes in question showing the greatest resistance to lack of 

 oxygen. We have then a fact that tends to contradict what has 

 gone before, for we have been proceeding upon the basis that 

 animals with a low rate of metabolism are more resistant to 

 lack of oxygen than are those with a higher rate. The explana- 

 tion of this phenomenon is not at present clear but it may be 

 that the contradiction is more apparent than real. The explana- 

 tion of how a fish with a high rate of metabolism can be more 

 resistant to lack of oxygen than one with a lower rate may be 

 found perhaps, in a qualitative rather than a quantitative investi- 

 gation of metabolism. Theories of anaerobic respiration suggest 

 that there may be present in the fish, previous to the breeding 

 season, large amounts of certain tissues that enter readily into the 

 securing of an oxygen supply from some source other than the free 

 oxygen. It is hoped that something may be done toward the 

 solution of this question in the near future. 



VI. SUMMARY. 



1. It has been shown that starvation in the rock bass (Amblo- 

 plites rupestris Raf.) produces first a rapid and marked increase 

 in the resistance of the starving fishes to lack of oxygen and 

 -/V/25,ooo KCN. Later th : s increase disappears and after 53 

 days of starvation the fishes that have been without food show 

 a considerably lower resistance to lack of oxygen and to KCN 

 solutions than do the controls. Furthermore, the starving fishes 

 are now less resistant than are fishes that have gone without 

 food for a- shorter period. 



2. The experiments with both lack of oxygen and with KCN 

 give results that place the fishes midway between the mammals 

 and the flat worms so far as the effects of starvation upon rate 

 of metabolism are concerned. In flat worms starvation initiates 

 and maintains an increased rate of metabolism up to death; 



