320 



Dr. L. T. Hogben and Mr. F. E. Winton. 



the posterior lobe, is produced by a principle probably identical with the 

 uterine stimulant, and is independent of the nerve-endings in the local effect 

 which it evokes. 



The normal reactions of melauophores to light in the frog depend on 

 several factors besides light, temperature being of predominant significance. 

 For the purpose of the experiments, it was necessary to use frogs in which 

 the melanophores were fully contracted. Decerebrated animals were 

 employed : the room temperature was uniformly 73° to 77° F. At this 

 degree of warmth, the frogs placed on a white background under bright 

 illumination show complete contraction of the melanophores, which con- 

 dition persists after the animals have been decerebrated carefully, so as to 

 avoid injury to the pituitary of the animal itself. Throughout this paper, 

 the melanophores referred to are in all cases the dermal melanophores. 



2. Specificity and Localisation of the Pituitary Mela/nophore Stimulant. 



The experiments recorded in subsequent sections were based upon 

 pituitary extracts prepared commercially for clinical purposes. Such 

 preparations are made from the posterior lobe of the gland, which includes 

 not only the infundibulum sensu stricto, i.e., the pars nervosa, but, in 

 addition, the pars intermedia, which is outogenetically a hypophysial 

 structure, though the term hypophysis is sometimes inaccurately applied to 

 the whole gland or to the pars anterior (anterior lobe) alone. Hence the term 

 iuf undibulin applied to such extracts is misleading. The following preliminary 

 experiments indicate the existence of a specific melanophore stimulant in 

 pituitary extracts and its localisation in the pars intermedia and nervosa : — 



(i) An adult female rabbit was decapitated, and its pituitary gland, 

 together with pieces of muscle, brain, ovary, pancreas, suprarenals and 

 spleen removed at once. The tissues were severally weighed, ground up 

 with sand, made up to 1 per cent, in Kinger, and left in the thermostat at 

 35° C. for 2 hours. At the end of 2 hours eight pairs of pale frogs were 

 taken, being injected in pairs (0 - 5 c.c. per individual), with the extracts of 

 tissues enumerated, another pair being injected with a 0*1 per cent, solution 

 of pituitary, and an additional pair with an extract of putrid meat. The 

 object of the latter injection was to control the possibility that the effects 

 found to follow injections of commercial products were not due to traces of 

 the physiologically active (pressor) substance known to occur in putrefying 

 tissues. After half an hour, the pairs injected with 1 per cent, and - l per 

 cent, pituitary extracts had assumed a coal-black hue, while all the others 

 remained pale : microscopic examination of the skin showed that this effect 

 was due to the expansion of the melanophores in the former case. 



