THE EXAMINATION OE MICRO-ORGANISMS 



623 



tubes, which will become filled during the sterilization. During 

 fermentation these become gas-holders. 



Blood Serum. 



Take blood from the jugular vein, operation wound, or placentc'e 

 with aseptic precautions, let it stand, draw off with large pipette into 

 test-tubes set on a slant. 



The serum sets after heating in hot-air sterilizer to 65° C 



Hearson's incubator, working with petroleum lamp. 



Gelatin Plate Cultures. 



Place three test-tubes containing nutrient gelatin in boiling water 

 until liquid, then cool to 40° C. Introduce into tube a sterilized 

 platinum loopful, a mere trace, of a culture of the organisms to be 

 examined, and mix well. Sterilize the loop, and put one loopful from 

 tube I to tube 2 and shake, put two loopfuls into tube 3 from tube 2. 

 Pour the contents of each into Petri dishes. In these the colonies may 

 be seen and counted without removing the lid. 



Agar plates are prepared in the same way, but it is necessary to 



