24 BACTERIOLOGY 



take it for granted that all pieces of apparatus not previously 

 sterilised are already contaminated with organisms from air or 

 water, fingers, or packing material, etc. Spores of moulds and 

 of bacteria, bacteria themselves, yeasts and other living 

 organisms are certain to be present, and mere " ordinary clean- 

 liness " such as washing removes only the excess of these 

 enormous numbers may be left on objects which to the eye 

 appear polished and clean in the ordinary household sense ; and 

 bacteriological cleanliness has a much more exacting standard. 

 Heat applied in some way or other, is the most commonly 

 used method of destroying all such contaminating organisms. 

 The direct flame may be employed, as for example in sterilising 

 the platinum needle with which the bacteriologist " handles " 

 bacteria. This (see Fig. 2) is a piece of platinum wire mounted 

 in a suitable handle. The end of the wire is either straight and 

 plain, or has upon it a loop with which the bacteriologist can 



lift a small amount of 



^ the bacterial growth or 



* i ~^i o a drop of the material 



c s -p containing the organ- 



Fio. 2. -Platinum "Needles." a. Ordinary fins, say, from one 

 Straight, for making stab-cultures, etc. tube to another, and 

 6. Ordinary Looped, for making surface with it he can also 

 cultures, etc. c. Long Straight, for making -i..,. QTYI V H nr film a 

 deep stab-cultures. mak:e smears or mms 



upon the glass slides 



for examination under the microscope. Platinum or some 

 cheaper substitute such as stiff electric resistance wire is 

 used for this purpose because it stands heating indefinitely, 

 and before and after use it is sterilised by holding it directly 

 in the flame of a Bunsen burner or spirit-lamp. Similarly the 

 points of forceps or any other instrument not spoiled by such 

 a procedure (e.g. hypodermic needles, etc., if made of platinum- 

 iridium) can be sterilised in the direct flame ; and of course it 

 is common knowledge that infected material such as bodily 

 excretions, old surgical dressings, and the like, are best dis- 

 posed of by burning. 



Many instruments and pieces of apparatus used by the 

 bacteriologist, however, cannot withstand exposure to the 

 direct flame, and dry heat in the form of hot air may be used 

 for such items as test-tubes, flasks, and other glass-ware, 

 copper and certain other metallic objects, etc. Of course 

 tempered steel instruments, rubber goods, etc., cannot be so 

 treated. A temperature of 160 or 170 C. is usually employed, 

 and is generally obtained by using a double-walled copper or 

 iron box like a small cupboard (see Fig. 3) which can be heated 

 most commonly by gas or electricity but it should be noted 



