362 WILLIAM H. COLE 



tion of the melanophores shows them to be contracted. This 

 condition, although beginning within an hour from the time 

 light begins to act, requires about two days for completion. On 

 a black background, however, in diffuse dayhght, the melano- 

 phores will remain expanded, but in direct sunlight on a black 

 background, they will contract. The absence of light produces 

 expansion. Animals with contracted melanophores were put 

 into complete darkness at room temperature. The course of the 

 expansion which followed was almost identical with that in the 

 temperature tests. At the end of two days the animals were 

 dark brown, due to the close network of the melanophore proc- 

 esses. When replaced in diffuse daylight, the former condition 

 was restored by the end of forty-eight hours. 



It was further found that distilled water, boiled water, or a 

 0.1 per cent solution of chloretone, all at room temperature and 

 in diffuse daylight, caused rapid expansion of the melanophores, 

 the maximal amount being obtained in about one-half hour. 

 Contraction is produced when the animals are replaced in tap- 

 water in the light. In other words, expansion of the melano- 

 phores of the frog tadpole may be produced by anoxemia — a con- 

 dition which is the reverse of that existing in the brook trout, as 

 described by Lowe ('17). One other condition inducing expan- 

 sion, observed frequently, is that of approaching death. Ani- 

 mals u}, a moribund state always show expanded melanophores, 

 regardless of temperature and illumination. Such dark animals 

 usually die after several days of subnormal behavior, although 

 they may recover and the melanophores return to their previous 

 state of partial contraction. 



Responses of these pigment cells to temperature, chloretone, 

 oxygen deficiency, and approaching death strengthen the hypoth- 

 esis that expansion is caused by a decrease, and contraction by 

 an increase in the metabolic rate of the whole animal. It may 

 be assumed that, at the normal rate of the various chemical 

 reactions going on in the body, certain substances specific for 

 melanophores are produced in the proper amount to preserve the 

 normal state of the pigment cells, whether this be a fully or only 

 partly contracted phase. Any change in the rate of these reactions 



