(9) Place the preparation between layers of filter-paper and dry by rubbing with the fingers, as one would in blotting ink.
(10) Put a drop of Canada balsam upon a clean slide, place the cover-glass film side down upon it, and examine with a one-twelfth objective. Cedar oil or water may be used in place of balsam for temporary preparations. Smears on slides may be examined directly with an oil-immersion lens, no cover being necessary.
Carbol-fuchsin is prepared by mixing 10 c.c. of a saturated alcoholic solution of fuchsin with 90 c.c. of 5 per cent. aqueous solution of phenol.
Gabbet's stain consists of methylene-blue, 2 gm.; 25 per cent. sulphuric acid, 100 c.c.
Both stains can be purchased ready prepared.
In films stained by Gabbet's method tubercle bacilli, if present, will be seen as slender red rods upon a blue background of mucus and cells (Plate II, Fig. 2). They average 3 to 4 µ in length—about one-half the diameter of a red blood-corpuscle. Beginners must be warned against mistaking the edges of cells, or particles which have retained the red stain, for bacilli. The appearance of the bacilli is almost always typical, and if there seems room for doubt, the structure in question is probably not a tubercle bacillus. They may lie singly or in groups. They are very frequently bent and often have a beaded appearance. It is possible that the larger, beaded bacilli indicate a less active tuberculous process than do the smaller, uniformly stained ones. Sometimes they are present in great numbers—thousands in a field of the one-twelfth objective. Sometimes several cover-glasses must be examined to find a single bacillus. At times they are so few that none are found in stained smears, and special methods are required to detect them. The number may bear some relation to the severity of the disease, but this relation is by no means constant. The mucoid sputum from an incipient case sometimes contains great numbers, while sputum from large tuberculous cavities at times contains very few. Failure to find them is not conclusive, though their absence is much more significant when the sputum is purulent than when it is mucoid.
| PLATE II |
| FIG. 1.—Heart-failure cells in sputum, containing blood-pigment, from a case of cardiac congestion of the lungs (Jakob). |
| FIG. 2.—A, Sputum showing tubercle bacilli stained with carbol-fuchsin and Gabbet's methylene-blue solution (obj. one-twelfth oil-immersion); B, sputum of anthracosis, showing particles of coal-dust stained with methylene-blue (obj. one-twelfth oil-immersion) (Boston). |
When they are not found in suspicious cases, one of the following methods should be tried:
(1) Take a few drams of the sputum in a test-tube, add hot water, and heat until the albumin is coagulated. Let settle for twenty-four hours, or centrifugalize at once, and examine the sediment for tubercle bacilli.