BACTERIA. 267 



we wish to define the outer limits of the jelly, which, in its 

 refractive relations, differs only little from water, we can readily 

 do so with the aid of Indian ink. The ink must be of good 

 quality, and should be ground down very carefully in water. 

 A drop of this ink can be placed upon the object-slide, the gela- 

 tinous mass which is to be investigated placed upon a cover-glass, 

 and the cover-glass then laid upon the drop. In this way the 

 particles of ink are prevented from passing between the jelly and 

 the cover-glass. The limits of the jelly are now sharply defined, 

 on account of the surrounding fluid being filled with fine particles 

 of ink which exert no injurious influence on the object. Such 

 masses of bacteria, embedded in jelly, are distinguished as zoo- 

 gloea, or the zooglcea Stage of the bacteriad. The jelly arises 

 from the swollen membranes of the bacteria, and in a number of 

 forms carbohydrates have been determined in it. It is quite 

 possible that the jelly taken into observation does not contain 

 these round " cocci," but shorter or longer rodlets (compare Figs. 

 102 and 104 A). The longer rodlets can be identified as composed 

 of shorter segments, which stand out very clearly if we add iodine 

 solution to the preparation. The segments now appear much 

 shorter than when in the fresh state, and partition walls are 

 shown which formerly were invisible. Such figures enable us 

 to form an opinion as to their mode of multiplication ; this takes 

 place by successive bipartition or fission, and the method has given 

 to bacteria the name of fission-fungi or Schizomycetes. The divi- 

 sions follow one another in the same direction, approximately at 

 like distances, and at right angles to the long axis of the organ- 

 ism. Only in a few cases, e.g., the Sarcina of the stomach, do 

 divisions take place at right angles with one another. 



The contents of the bacterial cells show a protoplasmic lining 

 layer and a vacuole, which in the elongated forms is broken up 

 by protoplasmic partitions or diaphragms. With present methods 

 of research no nucleus is identifiable. Most bacteria can be plas- 

 molysed by drying on the cover-glass, or by the aid of nitrate of 

 potash or sugar solution ; and to produce a rapid result pretty 

 strong solutions, e.g., 5 per cent, nitrate of potash or 10 per cent, 

 sugar solution, can be used. 



The protoplasm of the living bacterial cell is in general colour- 

 less ; only in a very few cases does it show a green colour from 

 chlorophyll (Bacillus viridis), or bright red (Beggiatoa roseo-persi- 

 cina), etc. With macroscopic observation, on the other hand, 



