October 3. 1890.] 



SCIENCE. 



18s 



of certain substances afl ministered as food, in changing the 

 color of tissues in some of the lower orders. In orange 

 canaries it has come to be an established fact, that, by feed- 

 ing the parent bird with a certain kind of food the active in- 

 gredient of which is cayenne pepper, the offspring will be of 

 an orange color; and orange-colored canaries may be seen in 

 the stores of most bird-fanciers. A food for producing 

 orange canaries is extensively advertised by a bird dealer in 

 Baltimore (Bishop). It is reported that the Indians of the 

 Amazon cause green parrots to change to yellow and red by 

 feeding them upon the fat of a certain fish allied to the shad.' 

 Dr. Merriam, in the letter previously quoted, says, "It is 

 well known that food affects the color in birds. Red purple 

 finches and pine grossbeaks invariably turn yellow when 

 caged. This is due undoubtedly to the absence of some im- 

 portant food-element. In some of the zoological gardens of 

 Europe it is the custom to send white spoonbills and flamin- 

 goes, to Amsterdam Garden to be recolored. The particular 

 food by which Mr. "Westermann accomplishes this end is 

 a secret, but it is believed to be a kind of shrimp or small 

 crustacean which has a quantity of red pigment in its shell." 



In the same direction are the changes of color in other 

 tissues by particular foods. It has long been known that 

 when pigs are fed on madder their bones become red. This 

 fact has been taken advantage of by physiologists in studying 

 the structure and development of bone. The phosphs.te of 

 lime acts on the coloring matter of madder as a mordant. 

 When given intermittently to a growing animal, the bone 

 presents alternate rings of red and white.^ 



Darwin^ mentions that pigs in Virginia eat the paint-root 

 {Lachnanthes tinctoria). and their bones are colored pink, 

 and it caused the hoofs of all but the black varieties to drop 

 off. "From facts collected by Heusinger it appears that 

 white sheep and pigs are injured by certain plants, whilst dark- 

 colored individuals escaped. . . . On asking some farmers in 

 Virginia how it was that all their pigs were black, he was 

 informed that the black members of a litter were selected for 

 raising, as they only had a chance of living.'' 



Fleurens ( 1824) made use of madder for coloring the semi- 

 circular canals of pigeons, to outline the canals more dis- 

 tinctly (see also Ferrier on "Functions of the Brain," and 

 the writings of Vulpin, the French physiologist). Mr. 

 Lucas, osteologist of the National Museum, informs me that 

 the bones of the crow are made purple by feeding on poke- 

 berries. Eidgway says the bones of the Western fox-squir- 

 rel are red, while those of its Eastern brother are white. No 

 cause has been assigned for the difference. See experiments 

 by Marci Paolini in 1841 ("Specimen quorundam experi- 

 mentorum de vi Rubiae ad ossa ovorumque Gallinarium 

 putamina calcarise coloranda," No. 1 of Miscellanii Medichi, 

 Pamphlet Vol. 1149). He gives a very good plate of the 

 colored skeleton of a fowl, and also of its colored egg after 

 four months feeding Rubia tinctorium. He also gives ref- 

 erences to other authorities, the most satisfactory of which 

 is Belchior ("Pliilosophical Transactions," vol. ix., 1732-44), 

 who gives an account of feeding hogs and fowls with madder- 

 root and wheat-meal. A rooster so fed died in sixteen days, 

 and showed the condition admirably. Other writers take up 

 the subject after him in the same publication. 



* Wallace's Amazon. 



= Todd's.Cyclopffidia of Anatomy and Physiology, Tol. iii. p. 863. 



3 Origin of Species, p. 9. 



It is reported that among workers in cobalt and indigo the 

 hair becomes blue; also, in artisans working with copper^ 

 the hair takes a greenish hue. 



The color of butterflies can be changed according to the 

 food upon which the caterpillars are fed. More remarkable 

 still, perhaps, is the change of color in the chameleon and 

 in many insects, according to the color of the substance with 

 which they are in contact. 



The environment undoubtedly has a powerful influence 

 upon the coloring of animals and birds. This is clearly 

 illustrated in every museum of natural history. Specimens 

 from arid desert regions are uniformly of a dull appearance, 

 compared with those from regions of luxuriant foliage. 



M. G. Pouchct,' in his work "Mechanism of Change of 

 Color in Fishes and Crustaceans," says that change of color 

 in fishes is due to the size of contractile colored cells placed 

 in the skin. These are under the influence of the nerves. 

 The author found that the particular nerves controlling 

 them (in the turbot) were nerves of the sympathetic system. 

 By cutting the nerve supplying a particular area of the skin, 

 he had been able to retain that area unchanged in color, 

 while the rest changed as the fish found itself on a dark or 

 light surface. That the eye is the means by which this 

 change in its condition is communicated to the fish or crus- 

 tacean, and that then reflex action takes place through the 

 sympathetic nerves on the color-cells of the chromatophors, 

 is proved by the fact, that, when the animal experimented 

 on is blinded, no further change of color occurs when it is 

 removed from light to dark or the opposite (see also Monthly 

 Microscopical Journal, 1871, vol. vi., M. G. Pouchet on 

 "Study of Connection of Nerves and Chromoblasts," imnci- 

 pally in fishes and batrachians). 



The reasons assigned by naturalists for periodica] change 

 in color of plumage or fur are twofold : (1) sexual selection ; 

 (2) as a protection against enemies. 



1. Sexual selection. The male takes on a brighter and 

 more attractive appearance to facilitate the business of 

 courtship and the securing of a mate. 



2. As a protection against enemies. In Arctic regions 

 birds and mammals are usually white in winter, the color 

 of the snow; so that they are with more difficulty found by 

 their enemies. Darwin supposes that originally only a few 

 individuals took on this change; and, these being better 

 protected, gradually, by a process of natural selection, only 

 the white variety was left. 



It is apparent, from what has been said, that there is very 

 much concerning the changes of color of the hair and other 

 appendages of the skin in man and the lower animals that 

 is not understood. In its normal condition, the color of the 

 hair is dependent upon the hair-bulb. It is here that the 

 melanine is secreted from the coloring-matter of the blood; 

 and from this point, as the hair grows, it permeates its cells, 

 the intensity and shades, from black to blond, depending 

 principally upon the amount of the coloring-matter. In 

 black hair the hair-bulb is larger, contains a greater amount 

 of melanine, and the hair itself is coarser and of more vig- 

 orous growth. In those cases where the hair has turned 

 from white to back, and minute examination has been made, 

 this has been found true. 



1 Transactions of the British Association tor the Adyajicement of Science, 

 1872, p. 162. 



