COLLECTION OF PUS. 137 



such circumstances unless the surface of the medium 

 has previously been coated with blood. 



Another method is to make gelatin plates. This is a 

 very simple matter if the materials are at hand. 



Requisites. i. Two or three tubes of gelatin. 



2. Two or three sterilised Petri's dishes. 



3. A platinum needle a loop will be best. 



Process. -Inoculate a gelatin tube in the manner de- 

 scribed on p. 22, and then melt it by immersion in 

 warm (not hot) water. 



Distribute the pus throughout the melted gelatin by 

 rolling the tube between the hands, and by tilting it 

 from side to side. Do not shake, and do not let the 

 melted gelatin touch the cotton-wool plug. 



Take a loopful of the gelatin and transfer it to a 

 second culture tube. Melt the gelatin in this and mix 

 as before. Proceed to inoculate a third tube from the 

 second one if you think it probable that the pus is very 

 rich in organisms. 



Now take the first tube and singe the projecting part 

 of the wool plug and heat the rnouth of the tube in 

 order to destroy any germs which may be upon it ; 

 allow it to cool. 



Place the Petri dish on the table in front of you and 

 raise the lid sufficiently to allow you to insert the end of 

 the test-tube ; do this, and tilt the latter so that the 

 melted gelatin flows into the dish. Immediately replace 

 the lid, and tilt and roll the dish until the gelatin forms 

 an even film over its whole lower surface. Place it on 

 a flat table to set. Repeat the process with the other 

 tubes. Incubate at about 20 C. for two or three days. 

 Examine the dishes, placing them on the stage of the 

 microscope and using the low power. Each organism 

 will have grown into a small colony, which will resemble 



