Effects of Caffeine and of Paraldehyde Upon the Color of the Frog.

Abstract

Incidental to studies on caffeine tolerance in the frog, it was noticed that frogs placed in 1:3000 caffeine solution for 30 to 90 minutes became darker than the controls in water. To test the matter further, frogs were made pale by placing them in water, in glass jars, on a white background, before the window or a strong electric light, as described by Hogben. 1 Caffeine was then added to one jar to make a concentration of 1:3000, a second jar containing water was used for the control frogs. The frogs in caffeine always became dark while the controls remained pale. The results were the same with frogs (R. pipiens) in spring, summer and fall of the year. Brown frogs of this species responded to caffeine with a more marked color change than did the green frogs. Injection, of onehalf cubic centimeter of 0.7 per cent NaCl solution containing 0.08 g. caffeine, into the abdominal lymph sac of 5 frogs of about 20 g. body weight also resulted in darkening. Hogben 2 reported that caffeine injections had no effect upon the color of frogs.

Microscopic examination revealed the fact that the webb melanophores were contracted before placing the frogs in caffeine solution, but were expanded after the action of caffeine was in evidence.

Sevrral investigators have shown a close relationship between the pituitary gland and the pigmentary system of frogs. 1 Therefore the entire pituitary gland was removed as carefully as possible by the method of Hogben 3 except that a hand drill was used to bore through the skull. The fact that the operated frogs became pale and remained pale when placed in darkness and moisture, was taken as evidence that the gland had been successfully removed.