184 



BACTERIOLOGY. 



by a test-tube. The method was introduced about the same 

 time by Bolton in this country, Globig in Germany, and 

 Roux in France. It is the method which is most often 

 employed when studying- the cultural characteristics on 



potato, of an organism. This is 

 because it is convenient and 

 simple in execution, and, like all 

 tube cultivations, almost entirely 

 free from danger of contamina- 

 tion. 



The large test-tubes (15 x 150 

 mm. ) should be employed. These 

 are cleaned, plugged, and steri- 

 lized in the usual way. A cork- 

 borer should then be selected 

 which will easily pass into these 

 tubes. In the absence of a cork- 

 borer, the student can easily im- 

 provise one out of a narrow test- 

 tube. For this purpose a sharp 

 file-mark is made, about three- 

 fourths of an inch from the end. 

 The end of a glass rod, which 

 has been heated in the flame of 

 a burner, or blast-lamp, till red- 

 hot, is then touched to the edge 

 of the file-mark. The glass 

 cracks, and leaves a clean cut 

 end. A piece of ignited char- 



FIG. 34. Tubes for cultivation on 



potato. ^-Ordinary form; b ROUX coal is better than the glass-rod 



form. 



since, by gently blowing, it can 

 be kept red-hot, while being held against the glass. 



Several large potatoes are brushed, under the tap, and 

 then steamed, or immersed in boiling water for 20 minutes. 

 A number of cylinders are then punched out of the cooled 

 potatoes. These cylinders (4-5 cm. long) should be placed 



