I2O BACTERIOLOGY. 



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 pro- 

 ducing any result. 



The protoplasm of some bacteria contains starch 

 granules ; thus Closlridium 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 

 pigment bacteria is probably external to the cell 

 as a rule ; for example, in Bacterium prodigiosum 

 the pigment granules are distinctly between the 

 cells ; on the other hand, in Beggiatoa roseo- 

 persicina, or the peach-coloured bacterium, the 

 special pigment bacterio-purpunn 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. 



Gelatinous envelope. In several species, either 

 as a result of a secretion from the cell, or of the 

 absorption of moisture and swelling up of the outer 

 layer of the cell-wall, a mucinous or gelatinous 

 envelope develops around them. This envelope 

 may form a capsule, such as we meet with in 

 certain bacteria found in the rusty sputum of 

 pneumonia, and in Micrococcus tetragonus ; or it may 



