MINUTER STRUCTURE OP BACTERIA 9 



of the higher bacteria, motility is probably due to contractility of 

 the protoplasm itself. 



The Minuter Structure of the Bacterial Protoplasm.— Many attempts 

 have been made to obtain deeper information as to the structure of the 

 bacterial cell, especially with reference to the existence of a differentia- 

 tion into nucleus and cytoplasm and as to the intimate phenomena of 

 division. Observations bearing on such points can only be made on 

 certain large species, but even with these, the minuteness of the cells 

 makes the interpretation of the appearances seen most difficult. While 

 bacterial protoplasm generally exhibits' a selective action for nuclear 

 aniline dyes, the material thus picked out appears in certain bacteria 

 not to be uniformly distributed through the cell, but to be deposited in 

 certain parts, and controversy has turned on the interpretation of such 

 appearances. Two main views are at present held by different schools. 

 Some consider that the bacterial cell contains a formed nucleus and a 

 cytoplasm ; at the same time it is questioned whether all the material 

 giving the reaction of a nucleus is really part of such a central structure 

 and not merely stored material. A modification of this view looks on the 

 nucleus as an extended thread lying in the protoplasm,— in some bacillary 

 types having a spiral or zigzag appearance. The other view is that 

 the bacterial cell represents a vital unit in which differentiation into 

 nucleus and cytoplasm has not yet occurred, and where the two main 

 elements of higher cells are still intermingled with one another, the 

 homologue of the cytoplasm being present in a close meshwork of 

 nuclear material. With regard to the behaviour of the cell in division, 

 amongst those who hold the former view some have figured appearances 

 in the supposed nucleus which suggest the occurrence of. mitosis, and 

 others consider that before division there is a longitudinal splitting of 

 the nuclear threads. All that can at present be certainly stated is that 

 there is frequently in the bacterial protoplasm material which reacts to 

 nuclear dyes, and material which does not so react, and that granules 

 occur which probably represent material in process of transformation for 

 the purposes of cellular nutrition. 



Before bacteria exceeding, say, 1 to 1*5 p in thickness were known, 

 appearances analogous to those described had been recognised among the 

 smaller forms, even when stained by ordinary methods. Occasionally 

 irregular, deeply staining granules had been observed in the protoplasm, 

 often, when they occurred in a. bacillus, giving the latter the appearance 

 of a short chain of minute cocci. These were called metachromatic 

 granules from the fact that by appropriate procedure they could be 

 stained with one dye, while the rest of the bacterial cell could be made 

 to take on another colour. Such an appearance is well known as 

 occurring in the diphtheria bacillus, especially when stained by Neisser's 

 method (p. 114). In certain bacteria, for example the plague bacillus, the 

 granules appear chiefly or solely at the poles and are often referred to as 

 polar granules. It will be gathered from what has been said that at 

 present it is impossible to interpret the significance of such granular 

 structures. The appearances are present in certain bacteria under all 

 circumstances, sometimes they are associated with growth in particular 

 surroundings. In some species the presence of granules- is an indication 

 of lowered vitality. 



Whatever the composition and relationships of the essential parts of 

 the bacterial protoplasm may be, there is, as has been said, reason for 



