54 METHODS OF CULTIVATION OF BACTERIA 



3 to 4 inches up, giving an oblique surface after solidification. 

 Thus agar is commonly used in such tubes (less frequently 

 gelatin is also " sloped "), and this is the position in which blood 

 serum is inspissated. Tubes, especially those of the less commonly 

 used media, should be placed in large jars provided with stoppers, 

 otherwise the contents are apt to evaporate. A tube of medium 

 which has been inoculated with a bacterium, and on which 

 growth has taken place, is called a " culture." A " pure culture " 

 is one in which only one organism is present. The methods of 

 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 



FIG. 14. Platinum wires in glass handles. 



a. Straight needle for ordinary puncture inoculations, b. "Platinum loop." 

 c. Long needle for inoculating " deep " tubes. 



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 2J 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. 

 " Taking a loopful " is a phrase constantly used. The third wire 

 (Fig. 14, c) ought to be 4^ 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 1J inches long, 2 mm. broad, and of 

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



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, 



