54 ILLINOIS ACADEMY OF SCIENCE 



oxysm in adjusting to the lower temperature; in any case the 

 time required to regain normality was always less in the case 

 of the smaller (younger) fishes of a given species. It will 

 be remembered that the reverse was the case with regard to 

 resistance to high temperatures. In no case was death the 

 result of sudden change from higher to lower temperatures, 

 though the widest range possible between the specific maximum 

 and freezing was tried. It may well be, however, that sudden 

 lowering in temperature does result in death where certain 

 species are concerned. In the planting of trout fry in cold 

 mountain streams, the change from the warm water of ship- 

 ping cans into the cold water of the stream has been blamed 

 for the high percentage of death on the part of the fry in some 

 cases. It is a common custom among fish culturists to cool 

 the water in the cans gradually down to the temperature of the 

 stream, by gradually adding the colder water to that in the 

 cans. Sudden changes from lower to higher temperatures 

 often result in marked temporary increase in activity, but 

 there is no loss of correlation of movements unless the higher 

 temperature is near the maximum for the species. 



In another series of experiments it was found that the time 

 which is required for a fish to become normal in cold water 

 is proportional to the time which it has been in the water of 

 higher temperature. This proportionality does not hold after 

 the fish has been in the warm water for more than an hour or 

 two, as the fish seems to become completely adjusted by that 

 time and further stay does not alter its actions when returned 

 to cold water. In one series of experiments of this sort, it was 

 found that if an adult Notropis blennius is transferred from 

 3° C. to 15° C. water for 1 minute and then back into the 3° 

 water, it is noticeably affected, but is normal within 1 minute. 

 If left in the warm water 5 minutes, is normal in 5 minutes 

 after being returned to the cold ; 10 minutes in warm, normal in 

 7 minutes in cold; 20 minutes in warm, normal in 10 minutes; 

 40 minutes in warm, normal in 15 minutes in cold. Up to 

 this point adults of this species always became normal in the 

 cold water without passing through the paroxysm. When 

 left in the warm water for 50-60 minutes, however, the par- 

 oxysm occurred 1 minute after transfer to the cold. Further 

 stay in the warm water had no increased effect except to in- 

 crease somewhat the total time elapsing before complete equi- 

 librium in the cold water was established. A single fish could 

 be made to pass through the paroxysm many times, the only 

 permanent adjustment upon the part of the fish being a slight 

 increase in its ability to resist the shock of the sudden change 



