14 LABORATORY EQUIPMENT 



Some part of the skin of the back is thoroughly disinfected and a well-fitting Bier 

 cup firmly applied. Suction arises and the skin assumes a dark bluish-red appearance. 

 After half a minute the cup is removed, the scarifier applied and the cutting edges set 

 free. The scarifier is then reapplied, but this time at right angles to the previous 

 incisions and the edges again set free. Suction is again made by the Bier cup and the 

 blood is thus forced out from the multiple incisions. 



The blood obtained by any of the above methods is collected into a 

 sterile vessel (graduate, flask, test-tube) and allowed to coagulate. The 

 clot is then separated from the sides of the vessel by a sterile glass rod or 

 platinum needle, the vessel plugged with absorbent cotton and placed into 

 the ice chest. After 12 to 24 hours the serum begins to separate out from 



FIG. 7. Obtaining blood by the wet-cupping method. 



the clot. If the serum is required immediately, the blood is allowed to flow 

 directly into centrifuge tubes, the clot separated from the sides and the 

 tubes centrifugalized. With a well-regulated centrifuge serum appears 

 after several minutes. 



There are several rules to be kept in mind when using a centrifuge. 

 Rules for i. The machine must be well oiled. 



the Use of 2. The counterbalance must be absolutely of the same weight. 

 Centrifuge. 3. The centrifuge should never be suddenly stopped, but allowed to do 



so of its own accord. 



4. In starting it, the motor should be gradually turned on. 



5. If the centrifuge is slightly out of order it should not be used, but repaired at 

 once, otherwise it may be ruined forever. 



6. One should never centrifugalize with cotton plugs in the test-tubes. If the 

 latter must be sealed, rubber stoppers should be used. 



