MELANOl'HORE A TYPE OF SMOOTH MUSCLE CELL 205 



Recently'^ I have found that the alkaline eartlis |)roduce a 

 contraction of the nielanophores in Fundulus. The time for 

 this contraction in isotonic solutions of the neutral chlorides 

 \aries in the order 



Ba < Sr < (^a < Mg 



In strontium, calcium and magnesiiun chloride, the contractions 

 are all reversible, the time required foi- complete recovery \'ary- 

 mg, in the reciprocal order — 



Mg- < Ca < 8r 



The behavior after treatment with 0.1 N HaCb for ten mimites 

 is peculiar in that, frequently, upon being returned to 0.1 N 

 NaCl, no sign of recovery appears for as long as thirty minutes. 

 After such a longer or shorter period of quiescence, the peripheral 

 nielanophores suddenly expand slightly and contract again al- 

 most immediately. After a brief inter\'al of inactivity, a sec- 

 ond expansion wave appears at the periphery, but this time the 

 nielanophores lying nearer the centre of the scale, which had 

 previously remained contracted, show a slight expansion and 

 those at the jieriphery expand further than the first time. In 

 this wa^^ there is set up a rhythmic expansion and contraction 

 wave which, creeping towards the centre of the scale, gradually 

 comes to include all the nielanophores. In the course of an liour 

 after being returned to sodium chloride, all the nielanophores of 

 a scale are slowly pulsating. This pulsation may continue at 

 ordinary temperatures for as long as four or five hours, the ex- 

 pansion gradually becoming less complete and frequent and 

 e\'entually ceasing, the nielanophores remaining contracted. In 

 cases where the immersion in BaCl2 has lasted only about five 

 minutes, the pulsations appear upon being retui'ned to NaCl. but 



'* In scale preparutioiis of b'undulus, the sinall deriiial Ijlood vessels always 

 contain a few corpusoles. When a scale is immersed in a KCU solution these cor- 

 puscles begin to move within the vessels and this movement continued approxi- 

 mately as long as the nielanophores are contracting. On being returned to NaCl, 

 the melanophores exj^and and the cori)Uscles return to tlieir original position or 

 ])ass beyond it. This movemi'nl of I lie corijuscles may l>c (hie to ;i conl rnction 

 and i-elaxation of the wnils of llic l;irgcr hlood-vessels. 



