II. CHEMISTRY 163 



sources. Goldblatt and Soames^^^ discovered that the Hvers of irradiated 

 rats, when fed to non-irradiated rats, convey some of the virtue of irradia- 

 tion to the animals which eat them. Hess et al.^ found that lanolin, the fat 

 of wool, is activatable, and Hess and Weinstock-* discovered that skin 

 itself becomes antiricketic upon irradiation and that irradiated cholesterol 

 is effective when administered subcutaneously. 



Rekling^®" found that irradiation did not protect rats from rickets when 

 they were prevented from licking their fur. Hou and Tso^''^ found that the 

 skin of normal rabbits was slightly antiricketic, the dorsal skin more so than 

 the ventral, but that the skin of rickety rabbits or of normal rabbits reared 

 indoors was without protective action. Hou^^- noted that the effectiveness 

 of ultraviolet irradiation for curing rickets in rabbits was almost lost when 

 the skin had been previously washed with ether. Rowan^^^ observed that 

 birds of prey on a meat diet developed rickets, and that the addition of 

 feathers to the diet supplied protection. He suggested that the preen gland 

 is concerned with the formation of vitamin D. Hou^^^ made an elaborate 

 study of the formation of vitamin D in birds. In brief, his findings were as 

 follows. Birds differ from mammals in having only one gland of a sebaceous 

 nature. This is the glandula uropygialis, or preen gland. Preen gland oil 

 contains provitamin D, which birds, by preening, distribute over their 

 feathers and effectively expose to sunlight. The vitamin D is either in- 

 gested by swallowing the feathers, or absorbed by the skin from the 

 feathers. The feathers and skin of normal birds were shown to be anti- 

 ricketic, but in rickety birds, or birds whose preen glands had been removed, 

 the feathers and skin had little, if any, antiricketic action. Removal of the 

 preen gland made the birds susceptible to rickets, and rickety birds without 

 the gland were not benefited by exposure to ultraviolet radiation or sun- 

 shine. 



Thus Hou^^^ was led to see that "... vitamin D or its precursor is princi- 

 pally derived from the oil secretion rather than from the diet. This may be 

 more or less true for all birds. For although nocturnal birds, and the car- 

 nivorous animals which prey upon other forms of 'feather and fur,' may 

 derive their vitamin D supply mainly from their victims, yet the source of 

 the vitamin in the prey would appear to lie in the oil secretion. This may 

 explain the absence of oil gland in some species of birds . . , and the necessity 

 of adding rabbits or small birds with the fur or feather intact, to the diet 



'" H. Goldblatt and K. M. Soames, Biochem. J. 17, 446 (1923). 



'«oE. Rekling, Strahlentherapie 25, 568 (1927). 



•" H. C. Hou and E. Tso, Chinese J. Physiol. 4, 93 (1930). 



'« H. C. Hou, Chinese J. Phijsiol. 4, 345 (1930). 



'"W. Rowan, Nature 121, 323 (1928). 



'" H. C.B.OU, Chinese J. Physiol. 2, 345 (1928); 3, 171 (1929); 4, 79 (1930); 5, 11 (1931). 



'" H. C. Hou, Chinese J. Physiol. 3, 171 (1929). 



