STAINING AND EXAMINATION OF MICRO-ORGANISMS 55 



even to some micrococci, offer yet greater obstacles 

 to exhibition by staining than do the spores. In fact, 

 to reveal the presence of these delicate thread-like 

 appendages by coloration, it is necessary to make use 

 of what is known to dyers as a mordant. The appli- 

 cation of this mordant or biting material enables the 

 nagella to subsequently fix the dye, for which they 

 have otherwise no affinity. It is to Loffler : that we are 

 indebted for the developments in microscopical tech- 

 nique which enable the nagella to be so easily and 

 beautifully exhibited in stained specimens. Loffler has 

 further found that in mordanting some varieties of 

 micro-organisms an acid, and in others an alkaline, 

 addition to the mordant must be made, and moreover 

 that the exact amount required varies in both cases 

 according to the particular organism under investiga- 

 tion. To render the mordant alkaline Loffler recom- 

 mends the use of a 1 per cent, aqueous solution of 

 sodium hydrate, whilst for the acidification of the mor- 

 dant he employs dilute sulphuric acid of such strength 

 that a given volume is exactly neutralised by the same 

 volume of the 1 per cent, solution of caustic soda. 



The following is the composition of the mordant : 



Solution of tannin (20 parts tannin + 80 parts water). 



To 10 c.c. of this tannin solution add 



5 c.c. of a cold saturated solution of ferrous sulphate and 

 1 c.c. of a concentrated solution, either aqueous or alcoholic, of 

 fuchsine. 



For many organisms the simple treatment with the 

 mordant is sufficient, but in the case of others, as before 

 mentioned, an acid or alkaline addition is requisite. 



After the preparation has been mordanted with the 

 above solution it is dyed as usual with the ' aniline- 

 water ' solution of fuchsine previously described. The 



1 Ceniralblatt f. BaTcteriologie, vol. vi., 1889, p. 209 ; also Ibid. vol. 

 vii., 1890, p. 625. 



