38 THE GROUSE IN HEALTH AND IN DISEASE 



and ia so far as it continues, pigmentation may be altered, but once the 

 circulation has ceased beyond the entrance to the base of the shaft, and once 

 that the feather, although still attached to the epidermis, is cut oft' from the 

 circulation in the deeper living layer of the skin, then the feather is no 

 more likely or able to change the pigment which is responsible for its pattern 

 or its colour than would be the same feather had it been plucked out and 

 kept entirely separate from the bird. 



Once the feather is full grown, and the circulation in it stopped, there 

 is no reason to believe that any thing can alter it save sunlight and water, 

 and oil supplied as an external unguent from the oil gland. That appearances 

 are most deceptive in this respect must be allowed. Feathers may be 

 collected from the flanks of hen Grouse which show every possible graduation 

 Pi menta- between the almost vermiculate flank feather indicating the perfect 

 tion. winter plumage, and the broad-barred breeding-season flank feather of 



the summer hen. But it is very much more probable that the growing period of 

 these ambiguous or intermediate feathers is one of great susceptibility to outside 

 conditions, as we know to be the case in respect of the metal lolic processes 

 which are taking place within the hen bird at the time. Pigment is indis- 

 putably a product of tissue metabolism. It is often probably a mere waste 

 product, but it appears at times to serve a special function notwithstanding. 

 It is also certain that pigment is a production whose appearance, or failure 

 to appear, is open to considerable vicissitudes in consequence of small 

 recognised changes in physiological condition, and of some less easily recognised 

 changes in the general metabolism of the body. 



In the hen Grouse during the breeding season we know that pigment 

 production is very actively at work, for we know that a very large amount 

 is being produced for excretion in the pigment glands of the lower part of 

 the oviduct. This pigment, moreover, is precisely of the shade and colour 

 which is characteristic, not of the breeding plumage, but of the winter dress 

 of the hen and the cock Red Grouse. It is normally deposited in al)undance 

 on every egg, but on the other hand it may abnormally fail to be deposited or 

 even produced at all, not only in the eggs in the oviduct, but in the circulating 

 blood of the bird's whole system. Thus the feathers, instead of becoming 

 bufl' or brown, reddish or even Ijlack as they proceed in growth, may be any 

 intermediate paler shade of bufl', or even white, a character which is due 

 generally to the complete absence of all pigment granules. The place of 



