FUNCTION OF CAEOTINOIDS IN PLANTS, ANIMALS 273 



appearance of the normally colored skin parts of these breeds of poultry 

 at the end of the laying season for the purpose of culling out the un- 

 profitable hens. This method of determining heavy from light laying 

 fowls is not applicable, of course, to the breeds of poultry, such as the 

 English Orpingtons, which never show yellow pigment in the visible 

 skin parts, although normally their adipose tissue and egg yolks are 

 colored with xanthophyll. 



Palmer and Kempster (1919b) made a study of the physiological 

 cause of the fading of the visible skin parts during egg laying. The as- 

 certaining of the correct cause of this phenomenon was made possible 

 by the success which wo had in raising a flock of pigmentless White 

 Leghorn fowls to maturity, the females showing normal egg laying ac- 

 tivity. It was found that xanthophyll appeared in the skin of non-lay- 

 ing fowls within a few days 3 after feeding xanthophyll-containing 

 foods, but that no pigment whatever appeared in the skin, and almost 

 none in the adipose tissue of the hens which were laying, although only 

 moderately (two eggs or less a week) , even after a month on xantho- 

 phyU-rich diets. The blood serum and egg yolks contained an abun- 

 dance of xanthophyll. It was also found that when pigmented fowls 

 which were not laying (in these cases cockerels were used) were placed 

 on carotinoid-free diets, they gradually lost the pigment from the visi- 

 ble skin parts in the same manner as laying hens. Histological studies 

 of the skin during this fading indicated that the movement of the pig- 

 ment was outward from the rete of Malphigi, where it is chiefly local- 

 ized, towards the epidermis. No evidence was obtained that the loss 

 of pigment was due to resorption but the indications were rather of 

 a normal replacement of epidermis cells by the columnar pigmented 

 cells of the Malphigian layer from beneath which carried less and less 

 pigment because the supply of pigment in the food had been cut off. 

 The fading of a highly pigmented skin is very gradual and usually re- 

 quires several months in the absence of carotinoid from the food or in 

 the case of egg laying. 



The collective data were interpreted to mean that the fading of the 

 skin during egg laying is the result of the deflection of the xanthophyll 

 of the food to the ovaries, resulting in a cutting off of the pigment 

 which would otherwise be excreted by the skin, the net result being the 

 same as if the xanthophyll was no longer being ingested in the food. 

 The writer believes that a continuous formation of ova, but not neces- 



In one case the color was distinctly visible in 72 hours after xanthophyll was intro- 

 duced into the ration. 



