6 MICRO-ORGANISMS AND DISEASE. [CHAP. 



larger or smaller masses of zoogloea, or when in the shape 

 of chains, the identification is not difficult ; 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 abso- 

 lutely insure, the diagnosis. These are the micro-chemical 

 reactions. The addition of liquor potassae leaves micro- 

 organisms quite unaltered, whereas fatty and most albuminous 

 granules alter or altogether disappear by it. Acetic acid 

 from 5 to 10 percent, 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 



