. Laboratory work in bacteriology. Bacteriology. COLIiODIUM SACS. 499 a test-tube and this is slipped inside of the sac. The first opening should be made in the bottom of the test-tube. A small narrow flame is directed against the bottom, and, when the glass has softened, it is tpuched with a piece of drawn-out glass-tubing which is then with- drawn. The glass adheres and-is drawn out into a thin capillary. This is then broken off at about cm. from the test-tube by a gentle tap with the glass-tube. The flame of the blast-lamp is then directed a,gainst the opening thus made. The broken edge
. Laboratory work in bacteriology. Bacteriology. COLIiODIUM SACS. 499 a test-tube and this is slipped inside of the sac. The first opening should be made in the bottom of the test-tube. A small narrow flame is directed against the bottom, and, when the glass has softened, it is tpuched with a piece of drawn-out glass-tubing which is then with- drawn. The glass adheres and-is drawn out into a thin capillary. This is then broken off at about cm. from the test-tube by a gentle tap with the glass-tube. The flame of the blast-lamp is then directed a,gainst the opening thus made. The broken edges sink to the level of the lube and a round opening results. In this way a large number of holes can be blown into the lower end of the tube which is then con- stricted in the manner already described. The finished perfor- ated tube ias the appearance shown in Fig. 71 e. The next step is to attach the collodium sac to either of these constricted tubes. The open end of the sac is trimmed square with scissors. The sac is then placed between filter-paper and dried by the application of gentle pressure. It is especially desirable to have the inside of the neck of the sac perfectly dry. The constricted tube is then in- serted into the sac up to where the constriction begins. This tube and- sac are now, carefully and cautiously, rotated in a horizontal position over a very small narrow flame. The modified Bunsen burner provided with a pilot light is especially useful for this purpose. The tube and sac are held at a distance of 3-5 cm. above the narrow flanje. The collodium contracts down upon the glass and forras a perfect con- nection. To make this absolutely tight the collodium, over the glass, should be rubbed with a heated rod. In the absence of the burner mentioned, a hot glass rod passed I'epeatedly over the end of the sac will cause this to adhere to the glass. A silk thread is then wrapped over this portion of the sac; and, finally it is thoroughly coated with collodium and a
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