INTRODUCTION: MORPHOLOGY 



aggregates of individuals. In many cases the zoogloeae and pellicles are 

 merely social aggregates of individuals *, just as a forest or a meadow is, 

 and, like these, cannot be considered as morphological units. In others, such 

 as the cloud-like mass shown in Fig. 3, or the delicate ramifying growth of 

 B. proteus (Fig. aa), we have a true 'colony' before us, whose shape is not 

 accidental, but a result of definite modes of growth and multiplication which 

 recurs regularly in every culture, the characters thus produced being 

 often of taxonomic value. In all such zoogloeae and pellicles each single 

 bacterium is independent of the others. The plant remains a single cell, 

 and there is never any division of labour such as occurs in the more complex 

 colonies of the lower plants (volvocineae) or animals (coelenterata). 



The bacteria are the smallest of all 

 known organisms, the most bulky coccus 

 having a diameter of only about 3/x (yow> mm -)- 

 Among the Staphylococci (the most widely 

 distributed pus-bacteria) the diameter is often 

 not more than o-8/x.and the volume accordingly 



only 



cub. mm. Inasmuch as the 



1700.000,000 



cell-substance contains a large proportion of 

 water, the weight, too, is inconceivably small ; 

 thirty billion would weigh only a gram. In 

 a drop of water 1 c. mm. in size, seventeen 

 hundred million pus-cocci would have room 

 and to spare. Even the comparatively large 

 anthrax bacillus is only 3-ioju long and 

 i-i-aju broad, so that its volume would have 

 to be increased eight million times before it attained the bulk of a middling- 

 sized cigarette. 





Fig. 3. Fragment of the botryoidal 

 zoogloea of an aquatic bacterium {Zoo- 

 gloea ramigera) of older authors. The 

 rods are thickly aggregated at the peri- 

 phery, less so in the middle ; they are 

 held together by mucus. Magn. 56. 



Compare the zoogloeae in Figs. 17, e t and 



'and h. 



Finer Structure of the Bacterial Cell (5). 



It would seem at first sight a hopeless task to attempt to gain an insight 

 into the architecture of so minute a thing as a bacterium. Nevertheless the 

 problem has been attacked, and, thanks to the efficacy of modern micro- 

 scopes, some new facts have been established. We might well suppose that 

 these organisms, standing as they do upon the very threshold of life, would 

 be of simpler structure than those elementary units, the cells, of which all the 

 higher plants and animals are built up. The first question then to be answered 

 is whether all those parts which constitute a simple cell, such as a plant-cell, 



* The word ' growth-form ' is often applied to these aggregates. This literal translation of the 

 German Wuchsform is an unfortunate one, inasmuch as the words growth and Wuchs do not connote 

 precisely the same ideas, and, furthermore, the expression is used by different authors in slightly 

 different senses (cf. Goebel, Outlines of Special Morphology of Plants, p. 480). 



