B. -Hamilton — Winter Whitening of Manimah and Birds. 309 



"We have then in winter whitening an instance of peripheral atrophy 

 of the hair or feathers — an atrophy which manifests itself more or less 

 in all the members of the Fauna of cold countries, and which may he 

 partial or complete, seasonal or permanent. 



I^ot the least remarkable feature of this atrophy of winter whitening 

 is the fact that the order of the parts affected by it is to all intents and 

 purposes the same in all mammals, even in those so widely separated 

 as the Stoat and Hare. Excluding, for purposes of this paper, the 

 head, the change begins from the base of the tail at the posterior 

 margin of the back, and on the flanks, just where the dorsal colour 

 meets the white of the underside. It then creeps up the back. In 

 many animals, as in British specimens of the Common Hare {Lepus 

 europoeus Pallas), which frequently whitens to a slight extent, it rarely 

 climbs higher than the rump. In spring the moult, and with it the 

 brown coloui", progresses in exactly the opposite order, creeping down 

 the back, and extending to the sides until it reaches the permanent 

 barrier of the white belly. It is, in fact, as if the internal physiological 

 condition represented by the white belly annually overpowers more 

 than its ordinary share of the animal in autumn, and in its ascent 

 reaches a height dependent upon its energy, to remain in possession 

 until driven out in spring by the way it came. 



I look iipon this fact as a confirmation of my hypothesis that 

 winter whitening is connected with the fat of the body and its distri- 

 bution. For it seems more than a mere coincidence that the upward 

 march of this winter whitening and the order of the parts affected by 

 it is almost exactly indicative of the order in which fat is accumu- 

 lated internally in an ox, sheep, or fowl — an order which is probably 

 applicable to other mammals and birds also. In oxen, sheep, and 

 fowls, as in man and most vertebrates, the favourite region for fat 

 storage is the belly, where, besides being deposited on the deeper 

 organs, such as the kidneys, it forms a layer known as the patmiculm 

 adiposes, lying near the surface, between the skin and the abdominal 

 walls. Next in order, as regards the accumulation of fat, comes 

 the rump, and thirdly, portions of the neck region and of the back 

 and ribs. 



And since we know that the presence of fat is indicative of defi- 

 cient oxydation, it is not altogether surprising to find external 

 atrophy its accompaniment. 



For the success of my theory two crucial tests have been suggested, 

 either of which might be performed by experiment. If my supposition 

 be true, there should (it has been thought) be more fat in hair in 



