V. ESTIMATION 



407 



thrombin level is less than half the normal, and it is probably less sensitive 

 to moderate reductions in prothrombin.-^ 



2. Blood-clotting time may be influenced by tissue juice or extract. It is 

 nearly impossible to avoid contamination with tissue juice completely by 

 any method of withdrawing blood samples that is not almost hopelessly 

 laborious when applied to a large number of chicks. 



0.2 0.6 1.0 1.4 1.8 



Log vitamin K dosage x 10 



Fig. 4. The relation of the reciprocal prothrombin time to the logarithm of the 

 vitamin K intake. Numbers have been multiplied by 10 for convenience in plotting. 

 Curves 1 and 2 from data by Almquist and Klose.^ Curve 3 adapted from data by 

 Stamler et al?^ Curves 4, 5, 6, and 7 from data by Quick and Stefanini.^^ 



3. Blood-(;lotting time may actually decrease in certain chicks after 

 severe loss of blood. For this reason it is not advisable to test all chicks for 

 blood-clotting time before administering supplements. 



4. Blood-clotting time is measured in periods from 2 to 30 minutes or 

 longer. It is often impossible to obtain any distinct values from certain 

 chicks with prolonged clotting time. 



To avoid the above objections, Almquist and Klose^ employed for vita- 

 min K assay the "prothrombin-time" method of Quick,"' -•* which depends 



" R. T. Tidrick, F. T. Joyce, and H. P. Smith, Proc. Soc. Exptl. Biol. Med. 42, 853 



(1939). 

 " A. J. Quick, Am. J. Physiol. 118, 260 (1937). 



