CHAPTER I. 

 BACTERIA. 



A BACTERIUM is a minute vegetable organism consist- 

 ing of a single cell principally composed of an albumin- 

 ous substance, which Nencki has called mycoprotein. 

 Nencki found the chemical analysis of bacteria in the 

 active state to consist of 82.42 per cent, of water. In 

 i oo parts of the dried constituents he found 84.20 parts 

 of mycoprotein; 6.04 of fat; 4.72 of ash; 5.04 of unde- 

 termined substances. 



Mycoprotein, which has the composition C 52.32, H 

 7.55, N 14.75, is a perfectly transparent, generally ho- 

 mogeneous body, which probably varies somewhat ac- 

 cording to the species from which it is obtained, the 

 culture-medium in which it is grown, and the vital 

 products which the organism produces by its growth. 

 Sometimes the mycoprotein is granular, as in bacillus 

 megatherium ; sometimes it contains fine granules of 

 chlorophyl, sulphur, fat, or pigment. Each cell is sur- 

 rounded by a cell-wall, which in some species shows the 

 cellulose reaction with iodin. 



When subjected to the influence of nuclear stains the 

 bacteria not only take the stain faintly, but in such a 

 manner as to show the existence of a large nucleus situ- 

 ated in the centre of the cell and constituting its great 

 bulk. The cell-wall generally is not stained, but when 

 it does tinge, a delicate line of unstained material can 

 sometimes be made out between the nucleus and the cell- 

 wall, showing the existence of a protoplasm. 



The anilin dyes, which possess a great penetrating 

 power, color the organisms so intensely as to preclude 

 the differentiation of the cellular constituents. Under 



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