40 BACTERIOLOGY 



test-tubes are sterilibed before filling, by placing them one 

 over the other in a wire crate lying on its side, in which 

 they are introduced into the hot-air steriliser and exposed 

 for an hour to a temperature of 100° C. [The cotton-wool 

 plugs should be inserted before sterilising.] 



The gelatine is introduced into the test-tubes with the 

 aid of a pipette, care being taken that it does not soil the 

 edge of the tube, and least of all comes in contact with that 

 part of the inner surface which supports the cotton plug. 

 In this manipulation the plug must be seized on the dorsal 

 surface of the hand between two fingers, and extracted from 

 the tube with a twisting motion ; the pipette is then filled 

 and closed with the forefinger, which is only raised when 

 the gelatine is to be allowed to run out into the tube. 

 After this procedure has been repeated a few times, each 

 worker in his own way acquires such a degree of expert- 

 ness, that the greatest possible celerity is attained in filling 

 the tubes with gelatine and quickly reclosing them. 



Instead of the pipette, the use of which always demands 

 a certain amount of skill, small glass funnels may aptly be 

 employed, or a glass tube capable of being closed by a tap 

 may be attached to the funnel through which the gelatine 

 is filtered and introduced into the test-tube to be filled. 



It is particularly to be observed that the gelatine 

 must not be kept continuously at a high temperature, lest 

 it should lose its power of solidifying when cold. It 

 must, therefore, be heated in the steam apparatus for 

 fifteen minutes on several — about three to five — days in 

 succession, in order that the culture-medium preserved in 

 the test-tubes may be completely sterile, and capable of 

 being stored for future use in all bacteriological experi- 

 ments. 



Preparation of meat extract peptone gelatine, — Hueppe's 

 meat-extract peptone gelatine is a 10 per cent, solution of 



