446 VITAMIN K GROUP 



Much of the data on which comparisons of time of action and kind of 

 vitamin K may be based were expressed in terms of the number or per- 

 centage of depleted chicks in which the blood-clotting time was reduced to 

 10 minutes or less in 18 hours after dosage. A clotting time of 10 minutes 

 probably represents a blood prothrombin level of only 20 to 30 % of nor- 

 mal.^" Nevertheless, the data obtained in these assays have comparative 

 value. The amount of vitamin Ki for a curative effect by these standards 

 was found to be approximately 1 7 per chick by several groups of investi- 

 gators.^- ^^> ^- The corresponding dose of methylnaphthoquinone Avas 0.3 7^^ 

 to 0.64 7.^^ With the same criterion of effect the curative dose in a 6-hour 

 assay was 1.5 7 of vitamin Ki and 0.5 7 of methylnaphthoquinone.^^ 



Later assays based upon the prothrombin-clotting time have shown that 

 5 7 of methylnaphthoquinone was sufficient to bring the blood prothrombin 

 content of a chick from 10 % of normal to normal in 4 hours.* In another 

 example, a 16 7 dose of methylnaphthoquinone was required for complete 

 recovery of prothrombin in 6 hours, whereas 8 7 gave about 50 % recovery.^" 

 In 18 hours the prothrombin was restored to normal by a dose of 6 to 8 7 of 

 methylnaphthoquinone while, at the same time, the whole blood-clotting 

 time was reduced to 2 minutes by as little as 1 7.^" 



In longer assays, 5 days or more, approximately 2 7 of methylnaphtho- 

 quinone daily per chick is required for a normal range of prothrombin.*' ^• 

 14, 15 Vitamin Ki at a daily level of 2 7 is insufficient,^* and the full require- 

 ment may be as high as 3.8 7* in the young chick. 



Qualitative requirement for the vitamin has been shown to exist with 

 several other kinds of birds.^® 



2. Rat 



Greaves and Schmidt^^ found that the low prothrombin in bile fistula rats 

 could be corrected by administration of a vitamin K concentrate. It was 

 difficult to deplete rats of vitamin K by dietary means, but eventually this 



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