26 BACTERIA. 



Exactly the same reactions are given when one of the 

 above colouring reagents or stains is added to a mass of 

 micro-organisms. The individual cells or organisms are 

 brought prominently into view, the central jelly-like speck 

 of protoplasm is most vividly stained in each, and reasoning 

 from analogy, certain authors have looked upon this active 

 part as the nucleus of the micro-organismal cell. Sur- 

 rounding the central protoplasm is a dense, sometimes 

 lamellated, thin skin or sheath which acts as a limiting or 

 protecting membrane. It very frequently contains a sub- 

 stance known as cellulose, almost, if not quite, identical 

 in composition with that forming the hard covering of 

 the vegetable cells that are found in the higher plants. In 

 other bacteria, in fact in the majority of them, the limiting 

 membrane seems to consist of a firm layer composed of 

 gelatinous material, sometimes stiff and rigid, or it may 

 be more or less elastic or pliable. Between the central 

 stained portion and the limiting sheath there sometimes 

 exists a narrow unstained area which by some is said to 

 be a space produced artificially by the chemical action 

 on the protoplasm of staining and other reagents ; others, 

 however, hold that it is a kind of modified protoplasm 

 which, surrounding the more active nuclear protoplasm, 

 divides it from the limiting membrane. Outside this limit- 

 ing membrane, or more strictly speaking, continuous with 

 it, there may usually be seen a mass of gelatinous or muci- 

 laginous matter which does not take on any special stain, 

 and which serves to separate the individual cells, or, to speak 

 more accurately, to bind them together into little groups. It is 

 due to the presence of this gelatinous material that we have 

 those frog-spawn masses or jelly-like lumps that are met 

 with in certain germ fermentative processes. These masses, 

 in which the organisms are embedded, as it were, in the 

 softened jelly-like part of their sheaths, are known as 

 zoogloea masses or masses of living glue. If the cells 

 remain isolated when the membrane becomes gelatinous, 

 capsules or highly refractile areas are seen around each 

 cell, when examined under the microscope. These may 

 sometimes be very delicately stained by certain methods 

 (Gram's method, see Appendix). As examples, may be taken 

 the capsule that surrounds the bacillus of pneumonia (Fried- 

 lander), the false Diplococcus of pneumonia and certain 



