322 



Dr. L. T. Hogben and Mr. F. R,. Winton. 



pallor which results from pituitary removal iu amphibian larvae, as shown by 

 Allen and others, is due to endocrine deficiency. 



3. Sensitiveness of the Melanophores to Pituitary Extracts. 



The following tests indicate the mode of response of frogs' melanophores 

 to different concentrations of pituitary extracts. Owing to the extreme 

 simplicity of the technique employed, it is not desirable to repeat the 

 description where experiments have been repeated for confirmatory purposes. 

 The extract employed was in all the remaining experiments Burroughs 

 and Wellcome's liquid sterile posterior lobe extract (" infundin ") in 

 - 5 c.c. tubes. 



(1) Solutions 05 per cent, - 05 per cent., 0'005 per cent., 0'0005 per cent, 

 of the liquid extract in frog's Ringer were made up, 1 c.c. of each solution 

 being injected into each of a pair of pale frogs ; a fifth pair was injected 

 with saline simultaneously as a control. At the conclusion of half an hour 

 (by which time maximum reaction is attained with pituitary extracts), the 

 two pairs injected respectively with 0'5 per cent, and - 05 per cent., showed 

 the striking pigmentary changes described in the last section ; the remainder 

 were still pale. On removing a piece of skin from the back of each frog, 

 fixing in Bouin's fluid, dehydrating and mounting in balsam, it was seen 

 that in the two pairs that showed visible darkening, the melanophores were 

 so fully expanded that their processes appeared to form a continuous web, 

 thus rendering the skin almost opaque. The other frogs showed complete 

 contraction of the melanophores, except in the 0'005 per cent, pair, in which 

 there was perhaps a very slight tendency towards a stellate condition of the 

 melanophores. The visible darkening of the skin appears within 10 to 

 20 minutes, reaches its maximum in half an hour, and disappears within 

 3 hours from the time when injection takes place, as was shown by a further 

 injection of the 05 per cent, solution into another pair of animals. Pieces 

 of skin were also placed in the stronger pituitary solution to test its action 

 on the isolated skin. So treated, they displayed on microscopic examination 

 half an hour later, complete expansion of the melanophores, while other 

 pieces placed in saline showed the melanophores contracted to fine points. 

 It should be explained, however, that if the skin is subjected to a good 

 deal of mechanical stimulation, as for example, after being cut into small 

 strips 2 mm. square, the melanophores remain contracted and will not respond 

 by expansion to pituitary extract. 



(2) A second tube of infundin was used to make up solutions, 01 per cent., 

 O075 per cent., - 05 per cent., - 025 per cent., - 01 per cent, and - 005 per 

 cent. Six pairs of frogs were taken and injected (0 - 5 per cent, per individual) 



