120 PHYSIOLOGICAL EEGULATIONS 



found water only by random movements ; once they touched it, the 

 depleted frogs stayed in it. Frogs that did not stumble into it 

 died of water-lack within a few centimeters of a life-saving pool of 

 water. I do not doubt that in outdoor life, frogs have cues that 

 guide them to water; those cues differ from the many that were 

 tested indoors. Though answers to none of the questions are re- 

 corded for the frog, certain observations have been made upon 

 another amphibian, Triton (Czeloth, '30). From a distance of 

 70 cm. the salamander moves directly toward a body of water. It 

 stays in contact with wet soil when possible, and frequents air of 

 high humidity without any liquid water being present. Neither 

 ocular nor nasal senses are required to detect either liquid or humid- 

 ity. All these actions are ones that result in preservation of the 

 animal 's water content. 



(3) Water might be expected to move outward through the skin 

 when an excess of water has been injected into the body. It does 

 not ; there is not even a decrease in the rate of movement inward in 

 the standard state (a). Of all the methods of influencing water 

 exchanges of frog that have been tested, outward passage of water 

 occurs only under the influence of solutes: (c) when a frog is put 

 into ''hypertonic" solutions (Adolph, '31b), and (d) when a frog 

 recovers (by being put into water) after a sojourn in a ''hypo- 

 tonic" solution of sodium chloride (new data). In both these cases 

 some exchanges of solutes are occurring. 



In a few words it may be said that dying frogs augment their 

 water intakes as much as living ones of the same water content; 

 frogs out of water lose excesses less rapidly than those immersed 

 in water; and water does not move outward through the skin, ex- 

 cept as it either evaporates or else enters a modified medium that 

 may allow exchanges of solutes. Undoubtedly many other physio- 

 logical states would likewise show water exchanges that differ from 

 those found in the arbitrarily chosen standard type of water load. 



"§> 40. Summary 



The equilibration diagram for water in the frog (fig. 66) is 

 characterized by a curve of losses that is proportional to water 

 content between - 10 and +30% of Bo, and a curve of gains that 

 has three limbs, being nearly horizontal at great deficits and in all 

 excesses, and steep at loads between and - 20% of Bq. Net gains 



