546 JACQUES LOEB AND HARDOLPH WASTENEYS 
tures. The term ‘indefinite’ means that the fish were alive and 
apparently normal at the end of the experiment. 
These experiments were repeated with the same material with 
approximately identical results; 33° was as a rule the upper limit 
the fish could resist during the month of January. Occasionally 
a fish would survive a sudden exposure to a temperature of 33° in 
a m/4 solution of NaCl + KCl + CaCl, but such fish were no 
longer normal and would swim on their side. 
It was next ascertained in which concentration the fish could 
resist the highest temperature. It was found that this concentra- 
tion was m/4. In m/2 and 2? m they were not able to resist as 
high a temperature as in m/4 or 2 m solution of NaCl + KCl + 
CaCl,. When sea-water was substituted for Ringer’s solution 
(NaCl + KCl + CaCl.) the results were the same as represented 
in table 1. 
TABLE 2 
DURATION OF LIFE OF FUNDULUS IN | | 
TEMPERA- Ay A: ee oad 5 URS DEX 
TURE | TROSE 
H2O | m/32 m/16 m/8 m/4 2m m2) |\ets | 
aa Bee : [eee eee aly NO A eee eee tee a | 
| | | 
29° 40’ | 40’ 30/ 40’ 100’ | 40’ 70’ AO el 
| 
31° 16’ 
we | allay 20' 20 | DA! 25’ 
The fact that the temperature which the fish could resist was 
the higher, the higher the concentration of the solution, suggested 
the possibility that the loss of water on the part of the fish in- 
creased their resistance. This explanation, however, does not 
agree with the observation made by Sumner and corroborated by 
us that Fundulus undergoes practically no change in weight when 
put into distilled water or when put back into sea-water. The 
idea that loss of water made Fundulus more resistant to heat 
could be tested by the substitution of sugar solution for Ringer’s 
solution or sea-water. It was found that dextrose solutions were 
not able to protect the fish, in fact such solutions were little if 
any better than H.O (table 2). 
The duration of life of the fish in the dextrose solutions is about 
identical with that in distilled water. This excludes the sugges- 
tion that osmotic phenomena determine the influence of the con- 
