516 PEEPAKATION, MOUNTING, AND COLLECTION OF OBJECTS 



It is used thus, viz. to 10 parts of solution B add one part of 

 solution A, and heat until vapour shows itself, then immerse the 

 whole cover-glass prepared as in the ordinary way for staining. One 

 minute suffices to stain the bacilli. Wash with plenty of water, and 

 after rinsing with distilled water drop on the film side of the cover- 

 glass a small quantity of solution C, which is not to remain more 

 than forty seconds. Wash off with plenty of water, dry, and mount 

 in xylol balsam. 



The bacilli will be found to be stained a fine rose-red upon a pale- 

 green ground. 



Staining Flagella. The following is the latest form of the cele- 

 brated method of Loffler. A mordant is made as follows : To 10 c.c. 

 of a 20 per cent, aqueous solution of tannin are added 5 c.c. of 

 cold saturated solution of ferrous sulphate and 1 c.c. of (either 

 aqueous or alcoholic) solution of fuchsin, methyl-violet, or ' Woll- 

 schwarz.' Cover-glass preparations are made and fixed in a flame 

 in the manner described above, special care being taken not to over- 

 heat. Whilst still warm the preparation is treated with the above 

 described mordant, and is heated in contact with it for half si 

 minute, until the liquid begins to vaporise, after which it is washed 

 in distilled water and then in alcohol. It is then treated in a 

 similar manner with the stain, which consists of a saturated solution 

 of fuchsin in anilin water (water in which a little anilm oil has 

 been shaken up and filtered), the solution being preferably 

 neutralised to the point of precipitation by cautious addition of 

 O'l per cent, soda solution. For some further details concerning this 

 process, the 'Journal of the Royal Microscopical Society' for 1890, 

 p. 678, may be consulted. 



Chemical Testing. It is often requisite, alike in biological and 

 in mineralogical investigations, to apply chemical tests in minute 

 quantity to objects under microscopic examination. Various con- 

 trivances have been devised for this purpose ; but the Author would 

 recommend, from his own experience, the small glass syringe already 

 described, or preferably the drop bottle, pp. 475-477, with a fine- 

 pointed nozzle, as the most convenient instrument. One of its advan- 

 tages is the very precise regulation of the quantity of the test to be 

 deposited which can be obtained by the dexterous use of it ; whilst 

 another consists in the power of withdrawing any excess. Care must 

 be taken in using it to avoid the contact of the test-liquid with the 

 packing of the piston. Whatever method is employed, great care 

 should be taken to avoid carrying away from the slide to which the 

 test-liquid is applied any loose particles which may lie upon it, and 

 which may be thus transferred to some other object, to the great 

 perplexity of the microscopist. For testing inorganic substances the 

 ordinary chemical reagents are of course to be employed ; but certain 

 special tests are required in biological investigation, the following 

 being those most frequently required : 



a. Solution of iodine in water (1 gr. of iodine, 3 grs. of iodide of 

 potassium, 1 oz. of distilled water) turns starch blue and 'cellulose 

 brown ; it also gives an intense brown to albuminous substances. 



/3. Chlor-iodide of zinc (Schultze's solution) is perhaps best made 



