I] MICROSCOPIC EXAMINATION 9 



clumps, such as larger or smaller masses of zoogloea, or 

 when in the shape of chains, the identification is not diffi- 

 cult ; but in the more isolated state they are not easily 

 recognised, owing, as a rule, to the presence of granules or 

 particles of various kinds, from which morphologically their 

 distinction is well-nigh impossible. In such cases there are 

 certain rules of thumb, if I may say so, which assist, although 

 they do not absolutely insure, the diagnosis. These are 

 the uniform size and shape and micro-chemical reactions. 

 The addition of liquor potassse leaves micro-organisms quite 

 unaltered, whereas fatty and most alb^iminous granules alter 

 or altogether disappear by it. Acetic acid from 5 to 10 per 

 cent, strong does not affect micro-organisms, but albuminous 

 and other granules become in most instances altered. These 

 two re-agents, I think, are as reliable as any others ; if they 

 fail, then others like alcohol, chloroform, sulphuric ether, 

 &c., are not of any greater help, but the latter re-agents may 

 be used, for instance, when it is a question between fat- 

 granules and micrococci, or crystals and bacilli. 



Micro-organisms have a great affinity for certain dyes, 

 especially aniline dyes, and therefore these are used with 

 great success to demonstrate their presence, and to 

 differentiate in many instances morphological details which 

 in the unstained condition are not discernible. The 

 staining is effected on fresh unaltered organisms, or after 

 they have been dried. In the first instance the process is 

 carried out thus : — A microscopic specimen is made, and to 

 it is added afterwards drop after drop of the dye, passing 

 it through the specimen in the usual way of applying fluids 

 to a microscopic specimen — i.e. by adding with a capillary 

 pipette the dye at one margin of the cover-glass and sucking 

 it up with a strip of filter-paper applied to the opposite 

 margin of the cover-glass. When the staining has taken 



