402 VITAMIN K GROUP 



K deficiency. Although crude sources of the vitamin would protect against 

 gizzard erosion, more purified fractions did not, nor did any of the known 

 vitamins. The existence of a separate unidentified anti-gizzard erosion factor 

 was shown. ^^ Further evidence on the non-identity of these factors was 

 found when it was observed that pure bile acids, especially cholic acid, 

 in the diet would protect the gizzard lining irrespective of large or no in- 

 take of vitamin K or prolonged clotting time.^^- ^^ Arachidonic acid has 

 been reported as the gizzard erosion preventive agent in fats.^^ 



Hypoprothrombinemia induced in chicks by vitamin K deficiency or by 

 adding dicoumarol to a practical diet does not furnish any histological 

 evidence of liver damage.^" 



V. Estimation 



H. J. ALMQUIST 

 A. BIOLOGICAL ESTIMATION 



The biological assay for vitamin K must be viewed in a somewhat differ- 

 ent light from that of certain other vitamins. General dietary deficiency 

 in humans is practically unknown, and only in a few pathological or emer- 

 gency conditions and in pregnancy is administration of the vitamin indi- 

 cated. Synthesis of the vitamin by microorganisms in the intestinal tract 

 is usually sufficient to supply the needs of most animals, except fowls. Ample 

 supplies of cheap synthetic forms and substitutes render dependence on 

 natural sources of minor importance. 



The assay methods therefore, are still primarily for research and may 

 differ greatly, depending upon the nature of the investigation. If intended 

 for the study of comparative potencies of vitamin K-active substances, a 

 relatively simple and convenient assay with the chick may suffice. On the 

 other hand, a study of the metabolism of vitamin K or of some substance 

 similar or synergistic or antagonistic to vitamin K may require a more 

 specific measurement of blood components and excretion products. For 

 general purposes it would seem advisable to employ an assay method which 

 is as simple as possible and which alters the blood from its natural compo- 

 sition to the least extent compatible with a degree of accuracy. No assay 



16 H. J. Almquist and E. L. R. Stokstad, Nature 137, 581 (1936). 

 " H. J. Almquist, Science 87, 538 (1938). 



i«H. J. Almquist and E. Mecchi, J. Biol. Chem. 126, 407 (1938); Proc. Soc. Exptl. 

 Biol. Med 46, 168 (1941). 



19 H. Dam, Acta Physiol. Scand. 12, 189 (1946). 



20 V. M. Emmel and H. Dam, Proc. Soc. Exptl. Biol. Med. 56, 11 (1944). 



