540 R. A. SPAETH 



tion was 1 part of sea-water to 14 parts of distilled water. This 

 solution is hypotonic to the plasma of Fundulus though no freez- 

 ing point determination of the blood of this species has been 

 made. It seems reasonable however that it should fall within 

 the range of the anadromous fishes which show a depression in- 

 termediate between purely marine teleosts (— 0.75°C.) and those 

 living in fresh water (— 0.53°C.). Assuming the A of the sea- 

 water used in this experiment to be as great as — 2°C. and that 

 this would vary directly with the dilution, a concentration of 1 

 part sea-water in 15 of solution would give a A of approximately 

 — 0.13°C. This is less than one-quarter of the value of the A 

 of fresh water teleosts, hence it follows that this dilution of sea- 

 water must give a solution hypotonic to the plasma of Fundu- 

 lus. If the effect of this dilute sea- water upon the melanophores 

 were an osmotic one we should expect it to be an hypotonic one 

 as was the case in pure distilled water, that is, it should cause a 

 contraction of the melanophores. As a matter .of fact in such 

 dilute sea-water the melanophores are expanded and remain so 

 for a considerable time (>1.5 hours) Hence it follows that in 

 sea-water there is a factor other than the hypertonic one which 

 inhibits the contraction seen in the melanophores when immersed 

 in distilled water. 



Experiments were next carried out upon the effects of the in- 

 dividual salts of sea-water. Sodium, potassium, calcium and 

 magnesium chlorides and magnesium sulphate were all used. 

 ' The concentrations varied from molecular to 0.01 molecular. 

 In the case of NaCl a few trials were made with as high a con- 

 centration as 2.5 M. 



These experiments showed conclusively that sodium chloride 

 is the only one of the five common salts of sea-water which causes 

 a lasting expansion of the melanophores. All of the other salts 

 produce a contraction. Hence it is sodium chloride which pre- 

 vents a contraction of the melanophores even in relatively dilute 

 (hypotonic) sea-water. ' Thus normal sea-water which is gener- 

 ally considered to be a balanced solution, that is, one in which 

 no specific ionic effect predominates over any other, upon dilu- 



