USE OF CULTURE MEDIA 49 



obtaining pure cultures will presently be described. When a 

 fresh tube of medium is inoculated from an already existing 

 culture, the resulting growth is said to be a " sub-culture " of the 

 first. All manipulations involving the transference of small 

 portions of growth either from one medium to another, as in the 

 inoculation of tubes, or, as will be seen later, to cover-glasses for 

 microscopic examination, are effected by pieces of platinum wire 

 (Nos. 24 or 27 Birmingham wire gauge the former being the 

 thicker) fixed in glass rods 8 inches long. 1 Every worker should 

 have three such wires. Two are 2 inches long, one of these 

 being straight (Fig. 14, a), and the other having a loop turned 

 upon it (Fig. 14, b). .The latter is referred to as the platinum 

 "loop" or platinum "eyelet," and is used for many purposes. 



FIG. 14. Platinum wires in glass handles. 



a. Straight needle for ordinary puncture inoculations. &. " Platinum loop." 

 c. Long needle for inoculating " deep " tubes. 



" Taking a loopf ul " is a phrase constantly used. The third wire 

 (Fig. 14, c) ought to be 4J inches long and straight. It is used 

 for making anaerobic cultures. It is also very useful to have 

 at hand a platinum-iridium spud. This consists of a piece of 

 platinum-iridium about 1^ inches long, 2 mm. broad, and of 

 sufficient thickness to give it a firm consistence ; its distal end is 

 expanded into a diamond shape, and its proximal is screwed 

 into an aluminium rod. It is very useful for making scrapings 

 from organs and for disintegrating felted bacterial cultures ; in 

 such manipulations the ordinary platinum wire is awkward to 

 work with as it bends so easily. Cultures on a solid medium 

 are referred to (1) as "puncture" or "stab" cultures (German, 

 Stichkultur), or (2) as "stroke" or "slant" cultures (Strichkultur), 

 according as they are made (1) on tubes solidified in the upright 

 position, or (2) on sloped tubes. 



1 Aluminium rods are made which are very convenient. The end is split 

 with a knife, the platinum wire is inserted and fixed by pinching the 

 aluminium on it in a vice. 



