172 



KNOWLEDGE. 



[ArcT-sT, 1901. 



a matter of common observation. I recollect picking 

 over two hundred of tlie fruits of the Hounds-tongue 

 off one stocking, after a stroll over the sand-hills that 

 fringe the mouth of the River Boyne. Think how the 

 sheep which graze on those sand-hills must cany the 

 seeds far and wide. The experience of finding one's 

 clothes full of the barbed finiits of the Enchanter's 

 Nightshade on returning from an autumn walk in the 

 woods is equally familiar to lovers of country rambles. 



HOW ARCTIC ANIMALS TURN WHITE. 



By E. Lydekker. 



Although I have not the details of any one particular 

 case before me, so many instances are chronicled in 

 which the hair of human beings, under the influence 

 of strong mental emotion due to terror or grief, has 

 hecome suddenly blanched within a single night or some 

 such period of "time, that the occasional occurrence of 

 such a phenomenon must apparently be accepted as a 

 fact. Such a change is, of course, due to the bleaching 

 of the pigment with Vvhich the hair is coloured, 

 although we need not stop to enquire by what particular 

 means this bleaching is accomplished ; all that coucenis 

 us on the present occasion being to know that the hair 

 in man may turn white in this manner under abnonnal 

 circumstances. And there appears to be evidence that 

 imder equally abnormal conditions a similar change may 

 take place suddenly in the hair of the lower animals. 

 This is exemplified by the well-known experiment made 

 considerably more than half a century ago by Sir John 

 Ross on an Arctic lemming — a small mouse-like rodent, 

 which habitually turns white in winter, although dark- 

 coloured in summer. In this instance the little animal 

 was kept in a comparatively warm room till winter was 

 well advanced, vVhen it was suddenly exposed to a tem- 

 peratxu'e of 30° below zero ; a continued exposure to 

 til is and a still more intense degree of cold eventually 

 lesulting in its death, which took place within three 

 weeks of the commencement of the experiment. In 

 consequence of- the conditions under which it had been 

 kept, this lemming was still brown in mid-winter, when 

 it ought to have been white. As a result of its 

 fii-st night's exposure, the fur on the cheeks and a patch 

 on each shoulder became completely white, and bv the 

 end of the first week the whole coat had turned white. 

 On examination, it was fovnid that onlv the tips of some 

 of the hairs had become blanched, and that these white- 

 tipped bail's were longer than the rest of the coat, 

 apparently owing to a sudden growth on their part, in 

 the course of the experiment. By clipping these long 

 whit^tipped hairs the animal was restored to its original 

 brown condition. 



Xothing is said with regard to any change of coat on 

 the part of this lemming previous to the experiment, 

 but it is probable that none occurred. It seems, how- 

 ever, to be clearly demonstrated that' the tips of the 

 hairs lost their colour by bleaching, induced by sudden 

 exposure to the intense cold, and that the hairs thus 

 blanched increased considerably in length in a very short 

 j'leriod. 



In spit« of the very obvious fact that these changes 

 occurred under extremely abnormal cii-cvimstances. it 

 has been argued that Arctic mammals which turn white 

 in winter do so normally by a similar blanching of the 

 hair of the summer coat, and that the greater length 

 of the winter, as compared with the summer dress of 



such white animals, is due to a lengthening of the 

 individual hairs of the former.* Moreover, it has been 

 inferred that the colour-change is directly under the con- 

 trol of the animals themselves. Quite apart, from many 

 other considerations, one weak point in this argument 

 is that the hairs in the subject of the experiment were 

 white only at their tips. It was doubtless assumed that 

 had the experiment been continued over a longer period, 

 the white would have gradually extended downwards 

 till the whole hair became blanched. But had this been 

 the normal way in which the change from a dark to a 

 white coat is brought about, it is obvious that animals 

 ought frecjuently to be captured in which the coat is in 

 the same condition as that of the lemming. So far, 

 however, as I am awai-e, no such condition has ever 

 been described. 



Moreover, it is perfectly well known that, apart from 

 those which turn white in winter, a large number of 

 animals have a winter coat differing markedly in 

 colour', as well as in length, from the summer di-ess. The 

 roebuck, for instance, is of a brilliant foxy red in sum- 

 mer, while in ^vinter it is grey fawn with a large patch 

 of pure white on the buttocks. And it is quite clear 

 that the change from red to grey, and the development 

 of the white rump-patch, is due to the shedding of the 

 short, summer coat and its replacement by the longer 

 winter dress. Obviously, therefore, it is natural to 

 expect that a similar change of coat takes jjlace in the 

 case of mammals which turn white in winter. 



That the change in spring from a white to a dark 

 dress is due to a shedding of the fur seems to be admitted 

 on all hands, for it would be obviously quite impossible 

 for long hairs to become short, or for white ones to 

 turn brown. And even in animals which do not alter 

 their colour in any very marked degree according to 

 season the spring change of coat is sufficiently obvious. 

 For the winter coat, owing to the long time it is worn 

 and the inclemency of the season when it is in use, 

 becomes much faded and worn by the time spring comes, 

 and the contrast between it and the fresh and brilliant 

 summer coat is very striking indeed. On the other 

 hand, the summer coat is only worn for a comparatively 

 short season, and that at a time of year when it does 

 not become much damaged by the effects of the weather. 

 Consequently no marked change is noticeable as the 

 long winter hairs grow up through it ; and it ha-s 

 accordingly become a common article of belief that, 

 whether there is a change of colour or not, the long 

 winter coat is produced by a lengthening of the summer 

 dress. 



Apart from the evidence of animals like the roebuck 

 and many other deer as to the existence of an autumn 

 change of coat, as deduced from a difference in colour, 

 the fact of such a shedding of the fur is demonstrated 

 by the circumstance that in many species, as, for 

 instance, the mountain hare, the individual hairs them- 

 selves, as seen under a microscope, differ appreciably in 

 calibre at the two opposite seasons. of the year. In that 

 species, for example, the hairs of the winter coat are of 

 a much finer character than are those forming the short 

 dress of summer, which are comparatively coarse and 

 thick. Moreover, in spite of the natural tendency to 

 believe in blanching on account of the afore'said 

 abnormal instances of turning white in a single night, 

 there is abundant evidence to show that even in human 

 Lair the change from dark to white as age advances is 



* See G. B. Poulton, " The Colours of Animals," cliapter vii. (1000). 



