BLOOD-SBKUM. 463 



Oxalateblood or plasma. — As is well known, the coagulation of blood 

 can be prevented by tlie addition of a small quantity of potassium 

 oxalate. The author has utilized this fact in order to obtain fluid 

 blood or unaltered plasma for culture purposes. 



A 6 per cent, potassium oxalate solution is prepared. The 

 capacity of the pipette (Fig. 63) is ascertained and the necessary 

 amount of oxalate solution is added so that the collected blood will 

 have 0.1 — 0.2 per cent, of potassium oxalate. Thus, if the pipette 

 can hold 25 c.c. of blood, then 0.8 c.c. of the oxalate solution should 

 be added in order that the resulting mixture shall contain 0.2 per 

 cent, of oxalate. The tube and contents are then sterilized in the 

 autoclave. 



Bef bre inserting the tip of the pipette into the artery, the 

 oxalate solution should be rolled so as to moisten the inner wall of 

 the pipette. This is then filled with blood and sealed according to 

 the directions given above. 



The pipettes can be placed in an ice-chest, in which case the 

 corpuscles will subside in 2 or 3 days, and, as a result, a perfectly clear 

 plasma can be obtained. This may be transferred by means of a bulb 

 pipette to sterile tubes. It can be used as such, or can be solidified 

 as in the case of bloqd-serum. 



Similarly, the fiuid blood itself may be placed in tubes and coagu- 

 lated at about 70°. The addition of 1 part of oxalate blood to 2 parts 

 of melted agar at 50° yields a bright red medium which can be solidi- 

 fied in an inclined position. This blood-agar is an excellent medium 

 for streptococci and other organisms. 



Blood-Serum. 



The serujn from the blood of the ox is frequently em- 

 ployed for cultivation purposes. The blood as it is ordin- 

 arily collected in the slaughter house is not sterile. If, 

 however, it is received into sterile vessels and kept covered 

 at a low temperature the few organisms that are present 

 will not multiply, and hence, a large proportiorl of the tubes 

 filled with such serum will remain sterile. 



The ialood should be received in battery jars which have 

 been covered with paper and sterilized! When the blood 

 has formed a solid clot, it is transferred to the ice -chest. 



