THE PREPARATION OF CULTURE MEDIA 11 



ing-tube, from which it is then transferred to the test- 

 tube. Care must be taken that the gelatine does not 

 come in contact with the sides of the test-tube near the 

 mouth of the latter, as this would cause the cotton- 

 wool stopper to stick to the glass and make it trouble- 

 some to remove. To prevent this the gelatine should 

 be poured from the measuring-tube into the test-tubes- 

 through a small sterilised glass funnel ; and this, if care- 

 fully done, will prevent the collection of any trace of 

 gelatine in the region of the stopper. After the tubes 

 are filled, and the stoppers replaced, they are at once 

 steamed for ten to fifteen minutes, which is repeated on 

 the two following days. 



To prepare sterile test-tubes for the reception of the 

 jelly new tubes should be soaked in hydrochloric acid^ 

 carefully washed with a brush, rinsed out with distilled 

 water, inverted to drain, then placed in a wire basket 

 and thoroughly dried in the hot-air oven (see fig. 3), 

 after which they are plugged with sterile cotton-wool 

 and then exposed to a temperature of from 140 to 

 160 in the oven for from two to three hours. The 

 cotton-wool used should be sterilised before plugging 

 the tubes by exposure to the same temperature in the 

 hot-air oven for two or three hours, until it becomes- 

 slightly browned, This separate sterilising of the tubes 

 and cotton-wool may appear tedious, but it cannot be 

 successfully dispensed with. 



Gelatine tubes thus prepared may be kept untainted 

 for an indefinite period of time. 1 



1 It must not be supposed that the gelatine -peptone medium thus pre- 

 pared will retain its properties absolutely unaltered for an indefinite 

 length of time, although for most purposes it may be used even months 

 after preparation. To reduce the chance of alteration in the gelatine 

 it should always be preserved in darkness, and before use the reaction 

 should be invariably tested, as it has a tendency to become acid on 

 keeping. This matter is of special importance in those cases in which 



