38 



COMPARATIVE PHYSIOLOGY 







work on the responses of pigmentary effectors. To Spaeth 

 (1914-1918), however, we owe the elaboration of an ingenious 

 method by which such observations may be made. Spaeth 

 fixes scales of the Atlantic minnow Fundulus in a glass container, 

 through which water circulates, on the mechanical stage of a 

 microscope. By connecting the adjusting screw of the latter 

 to a lever writing upon a smoked surface, the migration of the 

 pigment granules is recorded as the observer adjusts the screw 

 so that the distal extremity of the pigment mass is in alignment 

 with a particular scale mark on the micrometer (Fig. 13). 

 Melanophores of Fundulus do not react to visible Hght, but 

 they respond to electrical and chemical stimulation. Single 



make shocks do 

 not induce complete 

 contraction, but a 

 tetanising current of 

 moderate intensity 

 produces a complete 

 contraction, in which 

 the contraction phase 

 occupies 25-30 

 seconds and relaxa- 

 tion about 65-90 

 seconds. There is 

 a latent period of 

 about 5 sees, before contraction begins. Single make shocks 

 successively applied produce a summated effect if the inter- 

 vening period is not more than 2-3 sees. 



According to Spaeth, neutral electrolytes exert a specific 

 physiological action upon fish melanophores. Sodium chloride 

 (normal saline) promotes melanophore expansion ; while 

 potassium salts and salts of the alkaline earths bring about 

 immediate contraction. Distilled water always produces this 

 latter response. By combining these salts in such proportions 

 that their characteristic effects are balanced, Spaeth produces 

 a medium in which, after a preliminary contraction, the melano- 

 phores display partial expansion, so that, when a pharmaco- 

 logical reagent is dissolved in such a balanced solution, the 



Fig. 13. — Melanophoies of Fundulus (Spaeth). 

 (a) expanded ; (b) contracted. 



