3GO Dr. A. E. Wright and Capt. S. B. Douglas. [Sept, 1, 



Procedure No. 3, Employed where we desire to obtain Citrated Serum for 

 comparison with the Citrated Plasma furnished ly Procedure No. 2. 



Where we desire to obtain citrated serum for comparison with the 

 citrated plasma furnished by Procedure No. 2, we graduate our blood 

 capsule in precisely the same manner. Having filled in with blood 

 from the finger up to the first mark, we allow it to clot, and we then 

 introduce into the capsule from a capillary pipette a sufficiency of 

 citrate of soda solution to complete up to the second mark. Finally, 

 we churn up the citrate of soda solution with the blood clot and then 

 centrifugalise. 



Accuracy of the Method and Special Points which come up for consideration 



in connection with it. 



The accuracy of the method is attested b}^ the concordant results 

 set forth below of the large number of experiments which we con- 

 ducted in duplicate. We desire to point out that the results incor- 

 porated below represent not exceptional fortunate achievements, but 

 simply what may be obtained by the ordinary e very-day application 

 of the method. 



Before dismissing the consideration of the experimental method, it 

 may be well to elucidate very briefly three points which suggest 

 themselves for consideration in connection with it. 



The first of these relates to the calibre of the capillary tubes. 



In our earlier experiments we considered it advisable, with a view 

 to providing against a possible cause of fallacy, to conduct our experi- 

 ments in capillary tubes of a standard calibre. The tubes were in 

 each case calibrated by the method described by one of us,* to wit, 

 by introducing into the wide end of a tube drawn out in the flame 

 5 c.mm. of mercury from an " automatic pipette," and marking off that 

 portion of the capillary stem where this quantum of mercury formed 

 a column 5 cm. in length. The experiments which we conducted with 

 calibrated tubes are those which occupy the two next following sections 

 of this paper. 



In our later experiments, to wit, in the experiments which occupy 

 the later sections of this paper, we discarded calibrated for uncalibrated 

 tubes, making only the condition that the capillary tubes employed in 

 comparative experiments should appear to the eye to be more or less 

 comparable in calibre. It will be seen, on looking into our results, 

 that the concordance obtained was not less in the case where uncalibrated 

 tubes were employed than in the case where calibrated tubes were 

 employed. 



* "Transactions of the Roy. Medico-Chirurg. Soc.,' vol. 86, and 'Lancet/ July 5, 

 and Dec., 1902. 



