12 BACTERIOLOGY. 



give the reactions of myco-protein, and, therefore, is distinguished 

 as anthrax-protein. 



Considering bacteria as cells, we may speak of the cell-wall and 

 the cell-contents. The cell-wall consists of cellulose, or, according 

 to Nencki, in the putrefactive bacteria of myco-protein. It may be 

 demonstrated by the action of iodine, which contracts the proto- 

 plasmic contents, and renders the cell- wall visible. By staining 

 cover-glass preparations of the anthrax bacillus by the method of 

 Gram, the rods are at first uniformly stained, by subjecting them to 

 iodine solution the protoplasmic contents are contracted, and alcohol 

 decolorises the sheath, which may be then stained in contrast, with 

 eosin. 



The cell- wall may be either pliable or rigid. Pliability is 

 observed in the long filaments, which are endowed with a slow 

 vermicular movement, while rigidity accounts for the maintenance 

 of the characteristic form of several species, such as spirilla. 



The cell-protoplasm yields inyco- protein. In some it is homogene- 

 ous, and in others granular. The action of the aniline dyes indicates 

 a close relation to nuclear protoplasm, though all nuclear stains are 

 not suitable for bacteria. In some cases also the bacteria remain 

 stained under the influence of a reagent, which removes the colour 

 from nuclei. The power of fixing the stain is not always present, 

 and indicates a difference in the protoplasm of different species. 

 Thus in staining phthisical sputum, the nitric acid removes the 

 stain from all bacteria and bacilli present, with the exception of the 

 tubercle bacillus. This difference in the protoplasm of different 

 species is also illustrated by the necessity, in many cases, of using 

 special processes, owing to the ordinary methods being unsatisfactory 

 or not producing any result. 



The protoplasm of some bacteria contains starch granules ; thus 

 Clostridium butyricum gives the starch reaction with iodine. 

 Sulphur granules are present in some species of Beggiatoa which 

 thrive in sulphur springs. The colouring-matter of the pigmented 

 bacteria is probably external to the cell as a rule : for example, in 

 Micrococcus prodigiosus the pigment granules are distictly between 

 the cells ; on the other hand, in Beggiatoa roseo-persicina, or the 

 peach-coloured bacterium, the special pigment bacterio-purpurin 

 appears to be dissolved in the cell protoplasm. In Bacillus 

 pyocyaneus the pigment is certainly not localised entirely in the 

 cell, for it becomes rapidly diffused in the surrounding medium, 

 considerably beyond the confines of the growth itself. 



In several species, either as a result of a secretion from the cell or 



