CHAPTER X. — MORPHOLOGY OF THE BACTERIA. 455 



Little is known of the more intimate construction of the cells of the Bacteria, 

 owing to their minute size. All that can with any confidence be affirmed of the 

 greater part of them is founded less on direct observation than on the analogy of the 

 larger cells of other organisms, with which they agree in their chief characteristics so 

 far as these can be recognised, and with which they are also connected by inter- 

 mediate forms. 



The protoplasm of the cell in most forms and even in the larger ones appears, 

 when in a state of active vegetation, to be a homogeneous and faintly refringent 

 mass filling the cell-cavity. Distinct little granules (microsomata), the constitution 

 of which is still undetermined, may be distinguished occasionally in the larger 

 forms in this condition. They appear in greater abundance as the vegetative 

 activity diminishes, and the protoplasm may then be still more frequently seen to form 

 a parietal layer inclosing a pellucid central cavity. Highly refringent (crystalline) 

 granules of sulphur, which owe their origin to the decomposition of the sulphates by the 

 plant, are often imbedded in considerable quantity in the protoplasm of the species of 

 Beggiatoa which grow in springs containing sulphur, as was first pointed out by 

 Cramer and Lothar Meyer. 



The protoplasm of some species which appear to belong to this group forms 

 chlorophyll, and seems to be coloured green throughout by this substance. Van 

 Tieghem found two forms of this kind living in water, which he distinguishes as 

 Bacterium (Arthrobacterium) viride and Bacillus virens 1 ; W. Engelmann a third 

 marked by the very pale tint of its chlorophyll, which he names Bacterium 

 (Arthrobacterium) chlorinum 2 . 



Most species are distinguished by the absence of chlorophyll and analogous 

 colouring-matters. In this respect they agree with the Fungi, and it is owing to this fact 

 and its physiological consequences that they have received the name of Fungi. In 

 some species, Zopf's Beggiatoa roseo-persicina for example and its subordinate forms, 

 the protoplasm is uniformly tinged with a red colouring-matter, which Lankester has 

 carefully examined and named bacteriopurpurin 3 . It is not yet certainly ascertained 

 whether the colouring matters, which often give an intensely red, blue, yellow, or 

 other tint to the gelatinous accumulations of some small forms, such as Micrococcus 

 prodigiosus, are contained in the membranes only or are attached also to the 

 protoplasm. 



Some species which contain no chlorophyll form a substance in their protoplasm, 

 which from its behaviour with reagents and the physiological relationships observed in 

 certain cases, must be considered to be more or less like starch, or more correctly 

 granulose. The cells of Prazmowski's Bacillus (Clostridium) butyricus (Amylobacter 

 Clostridium, Tre'cul) and Spirillum amyliferum, van Tieghem 4 , become more highly 

 refringent in the stages which precede the formation of spores (section CXXX), and their 

 protoplasm then assumes a blue or violet colour with solution of iodine, either 



1 Bull. Soc. bot. de France, 27 (1880), p. 174. The figure there given by Van Tieghem from 

 Perty is interesting, but it must remain a question whether it belongs to this group. 



2 Bot. Ztg. 1882, p. 323. 



3 Quart. Journ. of Micr. Sc, New Series, XIII (1873), p. 408. 



* See Prazmowski, Unters. ii. d. Entwickgsg. u. Fermentwirk. einiger Faciei ienarten, Leipzig, 

 1880, and Van Tieghem in Bull. Soc. Bot. de France, XXVI (1879% p. 6,;. 



