RESISTANCE OF FISHES. 33! 



reaction to some extent but in the experiments the vigor and 

 frequency of the gulping was very noticeable, and gas bubbles 

 were often ejected at the gulps. The fishes now passed through 

 a period of alternating rest and activity. During the early- 

 phases of this period, activity was in the ascendency; later rests 

 occupied most of the time. The resting periods lengthened 

 with the gradual loss of equilibrium. The first sign of "stag- 

 gering" was a falling to a vertical position with the head up. 

 The fish gradually sank to this position and at first made swim- 

 ming movements which caused it to resume a horizontal position. 

 Later the restoratory movements were not made until the fish 

 came in contact with the bottom. Still later the contact stimulus 

 failed to cause a response and the fish came to rest on the bottom, 

 lying either on its side or on its back. The gill movements were 

 usually still strong and regular. The fish now lay on the bottom, 

 making only occasional swimming movements. 



In the low oxygen experiments, the movements of the fishes 

 often became convulsive and uncoordinated before equilibrium 

 was lost, and as time passed, this phenomenon became more and 

 more noticeable. Carbon dioxide, in the concentrations used, 

 did not cause much lack of coordination, but it has been demon- 

 strated that very high CO 2 (100 c.c. or more per 1.) will quickly 

 produce this effect. The effect of the carbon dioxide in the 

 concentrations used wt;s that of an anaesthetic which stimulates 

 in small amounts, or at first, but later anaesthetizes. In this 

 connection it was noted that the fishes that were the first to 

 succumb to the carbon dioxide were usually those that dis- 

 played the greatest activity. 



As the fishes became more and more overcome, the gills 

 developed irregularity in movement; gulps and extra large 

 opercular movements became frequent; later the gills became 

 more or less distended and stiffened, and the movements in- 

 frequent. Thus in cases where the gill movements averaged 

 9-10 in 10 seconds at first, there might now be an average of one 

 or less in the same period. At about this time the gill movements 

 took on a jerky mechanical appearance which continued until they 

 stopped altogether. In nearly all cases, after the gill movements 

 had stopped, life was still indicated by movements of the fins and 



