i8 MICRO-ORGANISMS AND DISEASE [chap. 



quite colourless. Only the syphilis-bacilli, tubercle-bacilli, 

 and leprosy-bacilli, are able to retain the dye ; other 

 bacteria lose it by being subjected to the permanganate. 



De Giacomi ' has improved this method of decolourising 

 by oxidation. Cover-glass specimens made of syphilis material 

 are stained with warm fuchsin for a few minutes, are then 

 washed in water to which a few drops of solution of iron 

 perchloride have been added, then placed into concentrated 

 solution of iron perchloride till the preparations have lost 

 all colour ; they are then stained for contrast in vesuvin or 

 Bismarck-brown. 



A. Gottstein^ places sections of syphilis material for 

 twenty-four hours in fuchsin or aniline water genetian-violet ; 

 wash with distilled water, then place them for a few seconds 

 into a pure or dilute solution of liquor ferri, then wash in 

 alcohol, clarify in clove-oil, mount in Canada-balsam. 



It may not be unnecessary to point out, that if sections are kept for 

 many hours in the staining fluid, there may be found in them micro- 

 organisms (particularly bacilli) which have been accidentally introduced 

 into them by the solutions of aniline dye. Many of these, particularly 

 when used alkaline, contain organisms, and if the sections are kept 

 in them for many hours, notably in warm weather, bacteria will be 

 found to have not only invaded the tissue but to have multiplied 

 therein. 



In examining fresh or hardened tissues for micro-organisms 

 it is necessary to make thin sections, which can be easily 

 done with the aid of any of the microtomes in common use, 

 amongst which Williams's microtome for ice or ether freezing, 

 Cathcart's for simple ether freezing, Minot's microtome and 

 the Cambridge rocker with ordinary razor for cutting riband 

 sections from paraffin-embedded hardened materials, are 

 easiest to manipulate. As a matter of fact we now use 



^ De Giacomi, Schweizer Correspondezblatt, xv. 12. 



2, A- Gottstein, Fortschrilte d. Medizin, Berlin, 1885, No. 16, p. 545. 



