1902.] the Bactericidal Power of small Samples of Blood. 65 



bottle and is kept sheltered from light. Before it is employed for the 

 purposes described below, it is sterilised by heating to 140° C. in a test- 

 tube, and is each time re-tested by shaking up with the dilute sodium 

 carbonate solution. 



Procedure adopted for obtaining from the Finger a Sample of Blood without 

 allowing this to come in contact with the External Air. 



A receptacle for the blood is first provided by drawing out a test- 

 tube to form such a " thimble " as is represented in fig. 5 (p. 66). 



The thimble is filled in with sterilised fatty acid-free oil, and is 

 covered in with a sterilised cover glass. 



The ulnar aspect of a finger — preferably of the little finger of the 

 left hand — is now sterilised by flaming alcohol. It is then punctured 

 in two or three adjacent points by a fine spicule of glass. A clean 

 handkerchief is wound round the digit, the tip of this last is immersed 

 into the oil, and pressure is applied to the finger pulp. The blood as 

 it emerges descends through the oil in the form of large globules. 



When pressure on the pulp ceases to yield blood, the finger is 

 momentarily removed from the oil, the handkerchief is loosened and 

 re-applied, the finger is re-immersed into the oil, and pressure is again 

 made on the finger pulp. 



"When a sufficiency of blood has been collected, a sterilised rubber 

 test-tube cap is drawn over the thimble. This last is then placed in a 

 hand-centrifuge, and the blood is, by a few turns of the handle, driven 

 down to the lower narrow end of the tube. 



After allowing an interval of 10 minutes to elapse, the centrifugalisa- 

 tion of the coagulated blood — the blood, it may be noted, invariably 

 coagulates* — is taken in hand. The contents of the thimble will now 

 arrange themselves into an upper layer of oil, a middle layer of clear 

 serum, and a lower layer of blood corpuscles. 



AVith a view to ensuring the asepticity of the further procedure, 

 the serum may now with advantage be separated from the oil in the 

 thimble, which has been exposed to some risk of aerial contamination. 



Procedure for the Separation of the Serum from the Oil in the Thimble 

 The procedure is as follows : — 



A series of three or four tubes, fig. 6, which are to function 

 respectively as receiving and mixing tubes, are flamed, filled in with 

 sterilised oil, horizontally inclined, and placed ready to hand. A 

 capillary testing pipette, similar to that figured (fig. 4) and described 



* (Added note.) The^ common text-book statement that coagulation is sus- 

 pended, when blood is collected under oil is, it maj bs presumed, based on experi- 

 ments undertaken with oil containing free fatty acids. A decalcification of the 

 blood might under such circumstances result. 



