LESSON V. 



INOCULATION OF MEDIA AND CULTIVATION OF 



BACTERIA. 



For convenience of description it is supposed that the student in the work of this 

 and the following two lessons is dealing with material containing but a single form of 

 microorganism and that the cultures obtained are pure, although- in practice this can 

 scarcely be expected to be realized. 



APPLIANCES FOR AND METHODS OF INOCULATION. 

 The Platinum Needle. There is no other appliance so constantly used in bac- 

 teriologic technique as the platinum needle. It is made by fusing into one end of a 

 glass rod the end of a bit of heavy (about No. 27) platinum wire, five or six centimeters 



FIG. 32. STRAIGHT PLATINUM WIRE AND PLATINUM WIRE LOOP. 



in length. Platinum and glass are employed for no other reason than that they lend 

 themselves readily to sterilization in the flame without danger of destruction. Any 

 sort of wire, as iron or copper, with or without a handle, may be substituted should 

 necessity demand such extemporization. A number of special shapes have been 

 suggested for the needle, but with a plain, straight wire and one twisted into a small 

 loop at the end (known as the "Oese" or "loop"), one may proceed without difficulty. 

 The loop is generally selected when a liquid material containing microorganisms is 

 to be conveyed to the nutrient medium, or when the substance to be inoculated upon 

 the medium contains relatively few bacteria ; it is used mainly for surface inoculations 

 upon the solid media and in inoculating liquid media. The plain needle is used when 

 the matter to be transferred is rich in bacteria, as in inoculating from an old culture 

 on solid medium to a fresh tube, and in making stroke inoculations and puncture 

 or stab inoculations. If bent at right angles to itself at the very end of the wire this 

 last needle is especially suited for picking out some special growth from a mixture 

 of colonies in an impure culture in order to transfer it to a fresh tube for the production 

 of a pure culture. In every use of the needle (Fig. 32) it must never be forgotten 



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