V. ESTIMATION 411 



Almquist and Kose,^* assaying the compound 2-methyl-l,4-naphtho- 

 hydroquinone diphosphoric acid ester in comparison to 2-methyl-l ,4-naph- 

 thoquinone by 4-day oral feeding to depleted chicks and comparison of 

 average prothrombin time 24 hours from the last dose, found the phosphoric 

 ester to be 1.5 times as potent as the quinone on a molar basis (one-half 

 as potent on a weight basis.) Assay of the identical preparations was made 

 by Lee et alP by subcutaneous administration, measurement of whole 

 blood-clotting time 18 hours from dosage, and expression of results as the 

 single dose required to bring the blood-clotting time of 50 % of the chicks 

 to 10 minutes or less. The phosphoric ester was found to be 50 % more po- 

 tent than the quinone on a molar basis in close agreement with the above 

 results. 



The potency of vitamin Ki was found to be approximately one-third 

 that of methyl naphthoquinone (Almquist^O- This ratio was also found in 

 an 18-hour curative assay by Fieser et al.~^ Emmett et al.,'^^ by the method 

 of Thayer et al.,^^ obtained 450 methylnaphthoquinone units per milligram. 

 Assays by the Dam-Glavind technique, as reported by Dam,- indicate an 

 average potency approximately 39 % of that of the methylnaphthoquinone 

 on a weight basis. 



Quick and Stefanini^^ have provided further data on the relative po- 

 tencies of these compounds in a 12-day preventive assay with chicks. These 

 data, plotted by the method of Almquist and Klose,^ are represented by 

 curves 4, 5, 6, and 7 in Fig. 4. Curve 4, obtained with methylnaphthoqui- 

 none dosages, has a slope of 1.35. Curve 5, obtained with vitamin Ki, has 

 a slope of 1.00. These curves converge at lower dose levels. The difference 

 between the curves at any prothrombin value or reciprocal prothrombin 

 time is the logarithm of the potency ratio of the two compounds. This ratio 

 is not constant. Curve 6 represents results from methylnaphthoquinone 

 dosage applied to chicks also receiving dicoumarol in their diets (p. 405). 

 As would be expected, the curve is displaced toward higher dose levels of 

 vitamin K; the slope of this curve turns out to be 1.35, however, the same 

 as in the absence of dicoumarol (curve 4). Curve 7 represents data from simi- 

 larly dicoumarol-poisoned chicks which received vitamin Ki. This curve is 

 also displaced toward higher vitamin K levels, but it has the same slope 

 as the vitamin Ki curve (5) in the absence of dicoumarol. Such agreement 

 could hardly be accidental. The remarkable consistency of these data is 

 brought out clearly by the graphical method of expression. 



The fact becomes evident that there is no constant ratio of activity for 

 methylnaphthoquinone and vitamin Ki. This ratio varies over a range 



3' J. Lee, U. V. Solmsseii, A. Steyorm:irk, and R. II. K. F'oster, Proc. Soc. Expll. 



Biol. Med. 45, 407 (1940). 

 <» A. D. Emmett, R. A. Brown, and O. Kamm, ,/. Biol. Chem. 132, 4G7 (1940). 



