The Pigmentary Effector System. 



321 



(ii) The small size of the pituitary gland in the rabbit as well as the fact 

 that the rabbit's pituitary is remarkably compact, having hardly any cleft 

 between the two lobes (which are thus additionally difficult to separate), 

 made it impossible to test the effect of extracts from different parts of the 

 gland in the foregoing experiment. In the case of the ox pituitary the 

 demarcation between the three parts is very striking. It was possible to 

 secure ox pituitaries from the slaughter house within little more than an 

 hour of killing, and to dissect away portions of the pars nervosa, intermedia 

 and anterior separately, for preparing extracts of the three divisions of the 

 gland. Each portion was weighed, ground up with sand, and after extraction 

 with Pdnger at 35° C. for 2 hours made up to a 01 per cent, and 0'02 per 

 cent, solution. A pair of pale frogs was injected with each of the six 

 solutions (0 - 5 c.c. per individual). After twenty minutes the four frogs 

 injected with anterior lobe extract showed no darkening. The pair injected 

 with weak (O02 per cent.) pars nervosa extract likewise displayed no 

 darkening, whereas both frogs which had been injected with - l per cent, 

 pars nervosa extract and all four animals injected with the pars intermedia 

 preparation (01 per cent, and 0'02 per cent.) showed intense darkening of the 

 skin. Microscopic examination showed that the three pairs injected respec- 

 tively with pars anterior, strong and weak extracts, and pars nervosa weak 

 extract, had the melanophores in the contracted condition, while the 

 remaining six, those injected with pars intermedia and pars nervosa strong 

 extract, displayed a state of general melanophore expansion of the 

 characteristic type. 



From these experiments it is clear that the pituitary gland contains a 

 specific principle which is capable of inducing an extreme type of melano- 

 phore expausion in the frog, and that the production of this substance is 

 located in the posterior lobe. It will be noted that the extract prepared 

 from the pars intermedia was in • the last experiment more potent than that 

 prepared from the pars nervosa in corresponding amounts of the fresh 

 glandular substance. The fact that workers like Swingle, who record the 

 effect of grafting experiments, claim for the pars intermedia an exclusive 

 role in the pigmental control of the pituitary gland, does not necessarily 

 conflict with this result, for it is on histological grounds unlikely that the 

 pars nervosa actually secretes the autocoid which produces melanophore 

 expansion. What is most likely, as has been suggested by other writers, is 

 that the pars intermedia secretion rapidly diffuses into the nervosa, in 

 which case the term infundibulin applied to such extracts is not merely 

 confusing but positively incorrect. The changes which follow injection of 

 pituitary extracts in the frog confirm the conclusion that the condition of 



vol. xcin. — B. 2 A 



