FISHES AND THEIR SURROUNDING MEDIUM. 301 



those cases in which they were transferred from a hypotonic or 

 isotonic medium to one which was strongly hypertonic. Nega- 

 tive results were indeed encountered at times, but very few which 

 could be regarded as contradictory. 



Extensive surface abrasions did not facilitate the influx or 

 efflux of water. The changes of weight in dead fishes were such 

 as to show that factors other than osmosis were concerned. 

 Dead fishes of most of the species used were found to gain in 

 weight in water of any degree of salinity up to the strength of 

 normal sea water. 



3 . Considerable changes in the salt [chlorine] content of the body 

 were likewise found to result, in many cases, from changes in the 

 salinity of the water. 



The problem here involved was attacked from both sides. In 

 the first place, the passage of salts (strictly speaking, of chlorides) * 

 into fresh water from fishes taken from salt or brackish water was 

 tested chemically. In the second place, the salt content of the 

 tissues of various fishes which had lived in water of various de- 

 grees of salinity was likewise determined. 2 It was found that the 

 results from these two methods presented some striking points of 

 agreement, though the latter proved, on the whole, to be much 

 more satisfactory. These changes in the chlorine content of the 

 body were frequently astonishing in their magnitude. F. Jietero- 

 clitus by both methods was found to part with about twenty-five 

 per cent, of its chlorine in the course of a single day. The loss 

 of chlorides from the body was, however, found to occur at a 

 steadily diminishing rate. 



The following table indicates the percentages of chlorine found 

 in specimens of F. diafhanns from brackish water (thejr habitat 

 locally) and in those kept for varying periods in fresh and in salt 

 water. The series is certainly suggestive. 



in days (8 fishes employed) 0.085 

 3 days (4 fishes employed) o. 108 

 I day (4 fishes employed) O.II2 



1 Mohr's silver nitrate titration method was here employed. The gain or loss in the 

 proportion of chlorine was held to be indicative of the behavior of the various saline 

 ingredients of sea water. 



2 It is needless to state that all fishes used in these two series of tests were previ- 

 ously thoroughly rinsed in fresh water. 



