Weigert (Gram’s Method).—In this modification aniline is substituted for alcohol, in order to avoid prolonged washing with the latter, and the process is conducted on a slide. The section is placed on a slide, stained with a few drops of gentian violet aniline water, prepared as in Gram’s method, the excess of fluid removed, and a few drops of Gram’s solution applied. Subsequently remove the liquid by gently blotting it off, then wash the section by allowing aniline to flow’ backwards and forwards over it, and when colour ceases to come away, repeat the operation with xylol for about 1 minute, then mount in balsam.
Weigert (Staining in Actinomycosis).—Immerse sections for 1 hour in Wedl’s Orseille stain, then quickly rinse with alcohol and counterstain with gentian violet. If it be desired to stain the mycelium also, afterwards submit the sections to Weigert’s modification of Gram’s method. See page 335.
Weigert (Staining Brain Tissue).—Pieces of brain and spinal cord are hardened in bichromate solution, followed by alcohol, then imbedded in celloidin or gum. If imbedded in celloidin, the pieces are subsequently taken from the spirit in which they are immersed, and placed for one or two days in saturated aqueous solution of copper acetate, diluted with an equal bulk of water, the mixture being kept at about 40° C. Afterwards transfer the pieces to 80 per cent. alcohol until required for cutting. Or, the sections can be cut first, and then treated with copper acetate. To stain the sections, after being well washed in 90 per cent. alcohol, they are transferred to Weigert’s hæmatoxylin and left from a few hours to two days, according to the differentiation required. When opaque and of a deep blue-black colour, they should be well washed for two or three days in distilled water. Next decolourise for 0·5 to 2 hours in a solution of 2 Gm. of borax and 2·5 Gm. of potassium ferrocyanide in 200 C.c. of water. As soon as the grey and white substances are sharply defined, again wash the sections in water for half an hour, then dehydrate, clear, and mount in balsam.
Woodhead’s Method of Staining Tubercle Bacilli.—Take a small quantity of sputum rich in bacilli, and spread it out by pressure between two cover-glasses, so that a fairly thin film remains on each. Then carefully slip one over the other until they come apart. Thoroughly dry the covers, and pass them rapidly three times through the flame of a spirit lamp, care being taken not to scorch the film, then float them face downwards on the staining solution, which has been previously prepared and filtered into a watch-glass. The stain should consist of saturated alcoholic solution of basic fuchsine, 1 part; absolute alcohol or rectified spirit, 10 parts; carbolic acid solution (5 per cent.), 10 parts. Leave the preparations in the watch-glass for 12 to 24 hours, unless time is an object. In the latter case heat the fluid gently until vapour is given off, then drop the films on the surface, and leave them for 3 to 5 minutes only. Next transfer the covers to an aqueous solution of sulphuric acid (25 per cent.), and when decolourisation is complete, as evidenced by the pink colouration not returning when the specimens are plunged into a bowl of tap-water containing a single drop of ammonia solution, thoroughly rinse in the slightly alkaline water and counter-stain in an aqueous solution of methylene blue. Finally, wash in water, carefully dry and mount in Canada balsam. The bacilli should stand out as bright red rods on a blue background of cells.
Ziehl-Neelsen (Staining Bacilli).—Sections are removed from weak spirit into Neelsen’s carbolic fuchsine and left for 10 or 15 minutes; next decolourise in sulphuric acid (sp. gr. 1·84) or nitric acid (sp. gr. 1·42) diluted with 3 volumes of water, rinse in 60 per cent. alcohol, and wash in a large volume of water to remove the acid. Tubercle and leprosy bacilli are the only micro-organisms that can retain the stain after treatment with acid. If the presence of traces of nitrous acid in the nitric acid be suspected, Squire recommends the use of saturated aqueous solution of sulphanilic acid mixed with one-third its bulk of nitric acid. The sulphanilic acid destroys any free nitrous acid, which would otherwise exercise a bleaching action on the fuchsine-stained bacilli. The sections may be counterstained with a solution of 0·5 Gm. of methyl green (or 0·25 Gm. of methylene blue) in 20 C.c. of rectified spirit and 80 C.c. of distilled water. Finally dehydrate in absolute alcohol, clear in cedar oil, and mount in balsam.
Appendix D.
THE METRIC SYSTEM OF WEIGHTS AND MEASURES.
The initial unit of the Metric System is the Metre or unit of length, which represents one ten millionth part of the earth’s quadrant, or one forty-millionth part of the circumference of the earth around the poles. The multiples and sub-divisions of this and all the other units are obtained by the use of decimals, and for this reason the system is also known as the decimal system. The multiples are designated by the Greek prefixes, deca = 10; hecto = 100; kilo = 1000; myria = 10,000. For the sub-divisions Latin prefixes are employed, as follows: deci = 1⁄10; centi = 1⁄100; milli = 1⁄1000. Thus for measures of length we have the following expressions, showing the abbreviations commonly employed, and the equivalents in the ordinary English standards of measurement—
| 1 | Myriametre, | Mm. | = | 10,000.0 | M. | = | 6.2137 | miles. |
| 1 | Kilometre, | Km. | = | 1,000.0 | M. | = | 0.6213 | mile. |
| 1 | Hectometre, | Hm. | = | 100.0 | M. | = | 109.362 | yards. |
| 1 | Decametre, | Dm. | = | 10.0 | M. | = | 32.8086 | feet. |
| 1 | Metre, | M. | = | 1.0 | M. | = | 39.3704 | inches. |
| 1 | Decimetre, | dm. | = | 0.1 | M. | = | 3.9370 | " |
| 1 | Centimetre, | cm. | = | 0.01 | M. | = | 0.3937 | " |
| 1 | Millimetre, | mm. | = | 0.001 | M. | = | 0.0393 | " |
From the unit of linear measure of metre is derived the unit of the measure of capacity or Litre. This represents the cube of one-tenth part of a metre, or a cubic decimetre, and its multiples and sub-divisions with their corresponding equivalents in Imperial fluid measure are as follows:—