4 MICRO-ORGANISMS AND DISEASE. [CHAP. 



specimens only. All one has to do is to draw up with a cap- 

 illary pipette or to take up with the point of a needle a drop 

 or particle of the material, to place it on an object-glass, and 

 to cover it up with a thin cover-glass. Where one has to deal 

 with liquids, such as artificial nourishing fluids, blood, serum, 

 tissue-juices, secretions, transudations, and exudations, no 

 addition is required. In the case of more solid material, 

 such as solid artificial nourishing material, bits of tissue, 

 &c., the addition of a drop of neutral previously well- 

 boiled saline solution (of 0'6 to 0'75 per cent.) is advantageous 

 although not absolutely necessary, since by pressing down the 

 cover-glass a layer of the material sufficiently thin for examin- 

 ation can be obtained. In some instances a bit of tissue can 

 be teased out into fine particles by means of two clean needles. 

 Where it is a question of micro-organisms sufficiently conspi- 

 cuous by their shape, size, and general appearance, their 

 identification in the fresh condition is not difficult ; this is the 

 case with bacilli, actinomyces, and mycelia, but in the case of 

 micrococci, especially when isolated or in couples, and lying in 

 blood, juices, or tissues, their recognition is often extremely 

 difficult. When in large clumps, such as larger or smaller 

 masses of zoogloea, or w T hen in the shape of chains, the identi- 

 fication 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 morpholo- 

 gically 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 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 per cent, strong does not affect 

 micro-organisms, but albuminous and other granules become 

 in most instances altered. These tw r o re-agents, I tliink, 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 



