3OO FRANCIS B. SUMNER. 



experiment the entire lot died throughout a period of from less 

 than a day to several weeks. 



In addition to a simple reversal of the normal medium (salt- 

 water fishes in fresh water and vice versa*) experiments were con- 

 ducted upon acclimatization, which was found to retard, but not 

 to prevent, the fatal effects of fresh water ; likewise with ^Mater of 

 a very low degree of salinity, which gave some of the most strik- 

 ing results to be recorded ; with fresh and salt ivater in alterna- 

 tion, in which case the fatal effects of the former were diminished 

 or annulled ; and with distilled water, which soon proved fatal to 

 F. lietcroclitus (the only species used). Surface abrasions (exten- 

 sive removal of scales) hastened the death of F. heteroclitus in 

 fresh water, but only exceptionally led to the death . of fishes 

 returned to full-strength sea water (again, contra Garrey) \ and 

 wrought no harm to fishes placed in very dilute brackish water 

 (three to four per cent, sea water), despite the fact that the latter 

 was without doubt strongly hypotonic to the fish. 



2. Considerable changes of weight ivere found to result, in many 

 cases, from changes in the salinity (Jicncc the osmotic pressure) of 

 the surrounding medium. 



The weighing operations were conducted with the following 

 species : Fundulus heteroclitns, F. majalis, F. diaplianus, Myoxo- 

 ceplialus octodecimspinosus, Microgadus tomcod, Pseudoplenronectes 

 americanus, Stenotomus clirysops, Ameiurus nebulosus, Lcuciscus 

 erytliropJitlialmus, Morone americana and OncorJiyncJius tsc/unvyt- 

 scha. During these experiments, the fishes were kept unfed, and 

 it is needless to add that abundant control experiments were per- 

 formed in order to determine the normal rate of loss through 

 waste. The changes of weight following changes in the density 

 of the surrounding medium were frequently surprisingly great, at 

 times as much as five per cent, or more in a single day. In many 

 cases, moreover, they were not accompanied by any apparent 

 harmful effect upon the fishes. With a very few exceptions, the 

 changes were such as to indicate that they were the result of 

 osmotic action. Thus, as a rule, the fishes gained in weight only 

 in solutions known to be decidedly hypotonic to their body fluids, 

 while with few exceptions a significant decrease only occurred in 



1 Op. df. 



