FINER STRUCTURE OF THE BACTERIAL CELL 



strongly to the glass and may by washing be freed from the fixative and 

 stained with haematoxylin or an anilin dye. Under this treatment all 

 bacteria, save the most minute forms, show the same structure (Fig. 5). The 

 membrane appears as a sharp outline enclosing a protoplasmic mass which is 

 smooth and homogeneous where it lines the membrane, but full of irregular 

 spaces (vacuoles) towards the centre. The protoplasm is uniformly stained 

 and shows no trace of finer details. Only the strongly refracting granules 

 already referred to take on a deeper tinge. Being similar in this respect to 

 the 'chromatic substance' of cell-nuclei, they are sometimes spoken of as 

 ' chromatin ' granules : a doubtful analogy at best. When the bacterial 

 cell contains only one such granule (Fig. 5, a, c, d, e) it certainly makes the 

 impression of a nucleus both as regards its size and its position in the cell. 

 But there are, just as often as not, several 

 granules in a single cell (Fig. 5, b, d,f), and 

 apart from the colour-reaction we have no 

 adequate reason for regarding them as nuclei. 

 They bear no relation to the process of cell- 

 division, and it is better to regard them merely 

 as granules of reserve food-stuff. All efforts to 

 detect a true nucleus have as yet failed, and it 

 is safer at present to look upon the bacterial 

 cell as being devoid of one. There is however 

 another view of the matter that has gained many 

 adherents. When bacteria are stained with 

 anilin colours they appear to take up more of 

 the stain than does the protoplasm of ordinary 

 plant-cells, and to retain it with greater tenacity 

 in the face of decolourizing reagents such as 

 alcohol and weak acids. Since moreover the 

 nuclei of all cells are distinguished by their 



avidity for colouring matters there has arisen the idea of a certain group of 

 substances, nuclear stains, that possess a peculiar affinity to nuclear substance. 

 This affinity is mythical. Nuclei take up all stains with more avidity than 

 the protoplasm does, and this behaviour rests probably not on the chemical 

 nature of the nucleus but on its physical constitution, such as its great density 

 and power of absorption. It is to the failure to recognize these facts that 

 the statement must be attributed which we meet with in almost all books on 

 bacteriology, namely, that the bacteria have a particular affinity to ' nuclear 

 stains' and that we are therefore justified in regarding them as primitive nuclei 

 devoid or almost devoid of protoplasm. Speculation followed speculation, 

 and, the bacteria being the simplest organisms known to us, the hypothesis 

 has been put forward that the first living things to arise on the earth were 

 similar naked nuclei, and that the protoplasm is the product of subsequent 



Fig. 5. Bacteria fixed with alcoholic 

 iodine solution and stained in various 

 ways, a and b t Cladothrix dichotoma 

 with sheath and one (a) or several 



(a 



(methyleneblue). _/, Spirillum- undula 

 (haematoxylin). All the figures show 

 the cell-structure described in the text. 

 Chromatin granules, black ; vacuoles 

 (sap-vacuoles), white ; protoplasm, stip- 

 pled. Magn. a-e 2250, f 1500. 



