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 

 100 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, * s 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. Bach 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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