ADAPTATION OF FISH TO TEMPERATURE 547 
centration found in the experiments with Ringer solution or with 
sea-water; especially if we consider the fact that Loeb found that 
.-Fundulus can live for over a month in an m/8 solution of dextrose 
at ordinary room temperature (if the solution is renewed every 
day). 
The difference between the results expressed in tables 1 and 2 
suggested that the protective action of the Ringer solution was 
of the nature of a specific salt action. We, therefore, tested the 
idea whether or not other salt solutions, e.g., NaCl or CaCl, 
could afford the same protection. It was found that this was true 
to a slight degree in the case of NaCl but not in the case of CaCl.. 
Table 3 may serve as an example. 
TABLE 3 
DURATION OF LIFE OF FUNDULUS IN | 
TEMPERS: 5 oe i - : - NaCl 
H2O m/64 m/32 | m/16 | m/8 | m/4 | } m | m/2 
29° 30’ 30’ | 40’ 50’ | indef. | 120 20 eo) 
ee eal) RE ee eal el elie SEMIN Didos 
H20 m/64 | m/32 m/16 m/8 m/4 | ¢ m CaCls 
29°" |) <20eamioogs |) 60"" | ont Were07" 4) 30”) 104) 
| [ | 
In an m/8 NaCI solution some but not all of the fish could live 
indefinitely at 29°; in an m/8 or m/4 solution of sea-water or Ringer 
solution they could all live indefinitely at 29°. We must therefore 
conclude that the protection which sea-water or a Ringer solution 
gives Fundulus against a high temperature is due to a specific effect 
of the combination of the three salts NaCl, KCl and CaCl in the 
right proportion. The idea presented itself that this protective 
action of the salts was the expression of an antagonism between 
the salts and a substance produced at a great velocity at a higher 
temperature, e.g., an acid. Experiments, to be discussed a little 
further on, on the immunization of fish against a high temperature 
eliminate this possibility. 
Experiments were tried on tadpoles and on a species of fresh 
water fish to ascertain whether these animals could resist high 
