226 



METHODS OF CULTIVATION 



3. Place the newly planted tube in the upright 

 position (e. g., in a test-tube rack) and allow it to 

 solidify. 



4. Label the tube; when solid, incubate. 



Esmarch's Roll Cultivation. 



1. Liquefy three tubes of gelatine by heat. 



2. Prepare three dilutions of the inoculum (as described for 

 plate cultivations, page 228, steps 4 to 7). 



3. Roll the tubes, held almost horizontally, in a groove made 

 in a block of ice, until the gelatine has set in a thin film on the 

 inner surface of tube (Fig. 120) ; or under the cold-water tap. 



FIG. 1 20. Esmarch's roll culture on block of ice. 



In order that the medium may adhere firmly to the glass, the 

 agar used for roll cultivation should have i per cent, gelatine or 

 i per cent, gum arabic added to it before sterilisation. 



Roll cultivations, which served a most important purpose in 

 the days before the introduction of Petri dishes for plate 

 cultivations, are now obsolete in modern laboratories and are 

 merely mentioned for the benefit of students, since examiners who 

 are interested in the academic and historical aspects of bacteriology 

 sometimes expect candidates to be acquainted with the method of 

 preparing them. 



The Preparation of Plate Cultures. 



If a small number of bacteria are suspended in lique- 

 fied gelatine, agar, or other similar medium, and the in- 

 fected medium spread out in an even layer over a flat 

 surface and allowed to solidify, each individual micro- 

 organism becomes fixed to a certain spot and its 

 further development is restricted to the vicinity of this 

 spot. After a variable interval the growth of this 



