i.] Structure of the Bacterium-cell. 5 



tained, because the individual cell is so small that it does not by 

 itself show any indications of colour. In some comparatively 

 large forms, those, for instance, grouped together by Zopf under 

 the name of Beggiatoa roseo-persicina, it can be seen that the 

 living protoplasmic body shares at least in the coloration, which 

 in this case is a bright red. Some of the colouring matters in 

 question have been submitted to closer examination and have 

 even received special names, as bacterio-purpurin, &c. In their 

 optical qualities they show various points of resemblance to 

 anilin dyes, as is indicated by the above name ; but we must 

 not infer from this that the chemical composition is analogous. 



Among other phenomena of frequent recurrence in the 

 structure and contents of the protoplasm the starch-reaction 

 claims special attention. Bacillus Amylobacter and Spirillum 

 amyliferum, v. T., in certain stages of their development have 

 this peculiarity, that a portion of their protoplasm, distinguished 

 from the remainder by being somewhat more highly refringent, 

 when treated with watery solution of iodine assumes an indigo- 

 blue colour like starch-grains, or speaking more exactly like 

 the granulose which forms a large part of their substance. The 

 conditions under which this phenomenon makes its appearance 

 and again disappears will be discussed at greater length below. 

 E.Hansen'sMicrococcusPasteurianus also and usually Leptothrix 

 buccalis show the granulose-reaction. We may also mention in 

 this connection the occurrence of sulphur-granules in Beggiatoa, 

 referring the reader to Lecture VIII for further particulars. 



The protoplasmic body of the Bacteria is surrounded by a 

 membrane or cell-wall. This membrane in one of the species 

 which have been examined, Sarcina ventriculi (see Lecture XI), 

 possesses, as far as is at present known, the qualities of typical 

 plant-cellulose-membrane; it is firm and thin, and assumes 

 the characteristic violet colour when treated with Schulze's 

 solution. But in the majority of cases there is no trace of the 

 characteristic coloration of cellulose. In single specimens 

 scattered about in a fluid the membrane appears under the 



