542 . R. A. SPAETH 



of atropine sulphate from time to time. The atropine sulphate 

 is a more violent and rapid expansion stimulus than NaCl which 

 was used in other experiments of the following type. 



Octobei- 19, 1912 



8.52 A.M. Scales from a 10 cm. female were placed in distilled water. 



9.02 A.M. All the melanophores were contracted. Scales were now 

 immersed in a 1 per cent atropine sulphate solution at 

 9.05, 9.22, 9.28. 9.30, 9.35, 9.40, 9.44 and 9.59. The first 

 six trials all showed an expansion clearly except the 9.30 

 scale. 



9.44 A.M. The expansion was very slight. 



9.59 A.M. No expansion. All scales remaining in distilled water 

 showed the characteristic half expanded condition at 

 this time. T. = 19°C. Thus at room temperature the 

 melanophores lose their irritability completely after an 

 exposure of approximately an hour in distilled water. 



The results of the foregoing experiments with sea- and dis- 

 tilled water may be summarized as follows: 



1. In sea-water practically no migration of pigment occurs 

 either in expanded or contracted melanophores. 



2. In distilled water, scales from a light fish show (a) an ex- 

 pansion; (b) a contraction; (c) a secondary expansion and fin- 

 ally (d) degeneration in the melanophores. The first response 

 (a) is due to the elimination of the inhibiting nerve tonus and is 

 independent of the specific effects of distilled water (b-d). This 

 characteristic cycle of reactions is completed in less than an hour 

 at room-temperature. There is evidence for a selective absorp- 

 tion of water by the melanophores which may be the cause of 

 the contraction (b). 



3. A gradual dilution of sea-water by the addition of distilled 

 water causes a corresponding expansion of the melanophores. 

 The greater the dilution the longer does this expansion last — 

 up to an optimum concentration. Beyond this, as the propor- 

 tion of sea-water in the mixtures diminishes, the cytolytic effect 

 of the distilled water becomes evident in the decrease of the dura- 

 tion of the expansion. Finally, at a dilution of one part sea- 

 water to 50 of distilled water, the initial contraction is practically 

 indistinguishable from that in distilled water but the presence 



