FORMS OF BACTERIA 13 



5. THE INTERNAL STRUCTURE AND CONTENTS OF 

 THE BACTERIAL CELL. 



Although these organisms are very minute, some headway has been 

 made in our knowledge of the structure and contents of the bacterial 

 cell. Like all other organisms, bacteria possess within their cells that 

 substance which is the seat of life, viz. protoplasm. This protoplasm 

 in bacteria is usually enclosed by a protective membrane or cell-wall, 

 which is secreted by the protoplasm. The cell-wall bears the same 

 relation to the protoplasm that the nails of our fingers bear to the 

 living substance of our fingers. 



We do not know the structure of protoplasm, for it cannot be 

 analysed without being killed, and when it is killed the structure 

 is altogether changed. This applies to the structure of protoplasm 

 generally, and not merely to that of bacteria. We know, however, 

 the chemical elements that enter into its composition. These are 

 carbon, oxygen, hydrogen, nitrogen, sulphur, and phosphorus. Now, 

 in all living creatures, protoplasm is being constantly built up, and 

 again broken down into simpler substances. Its production conse- 

 quently necessitates a constant supply of mw materials of different 

 kinds. These constitute the food of an organism. As the raw material 

 is not changed into protoplasm at one step, there will be a number 

 of substances inside the cell, intermediate between raw material and 

 protoplasm. These we may term intermediate products. Then again, 

 when the protoplasm breaks down, another set of different substances 

 is formed. There will, therefore, be a large number of substances 

 inside the cell, as a result of these two processes. Then it must be 

 remembered that many of the substances absorbed as raw material 

 cannot be used as food in the form in which they are absorbed, 

 and therefore they are changed into the appropriate form by sub- 

 stances called ferments, which will be treated more fully in a later 

 chapter. 



Further, protoplasm is sometimes specialised, portions of it being 

 set apart to perform certain functions. Thus, in higher plants, a 

 specialised part, called the nucleus, is mainly concerned with the repro- 

 duction and multiplication of cells, and as another example may be 

 mentioned the clilwopliyll corpuscles, which cause the colour of green 

 plants and are concerned in the elaboration of plant-food. We shall 

 now proceed to what has actually been discovered in the case of 

 bacteria. 



