THE MORPHOLOGY OF BACTERIA 3 



In the sulphur bacteria the cell plasma may contain certain 

 glistening, strongly refracting granules which are soluble in 

 bisulphide of carbon, alcohol, xylol, and the alkalies. They 

 consist of pure sulphur, and are products of the reduction of 

 sulphur compounds found in the waters in which they abound. 



Again, in certain bacteria the cell plasma may be tinged with 

 color, either green by a chlorophyl-like substance, as in Bact. 

 viride, and B. virens, Van Tieghem, and Bact. chlorinum, Engel- 

 mann ; or by a violet-brown pigment known as bacteriopurpurin, 

 as in Chromatium Okenii, Rhabdochromatium fusiforme, and 

 other species described by Winogradsky. 



B. The Capsule 



The capsule consists of an inner tougher portion immediately 

 surrounding the central body, and which gradually passes into a 

 thinner and more watery outer portion which is uncolored by 

 ordinary staining methods. 



This outer portion of the capsule is furthermore so delicate 

 in structure that it is easily destroyed or altered. Thus in the 

 drying of films upon cover-glasses it shrinks to a fraction of its 

 original thickness, or when in contact with water is subject to 

 dissolution. Its failure to stain with the ordinary colors has 

 caused it to be overlooked by most bacteriologists. It is well 

 known that if bacteria are stained with aqueous analine dyes, 

 only the central body is colored, and perhaps a portion of the 

 denser part of the capsule. If, on the other hand, the same 

 bacteria are stained by Lowit's method (see p. 6), it will be 

 noted that the bacilli are as a rule larger and plumper, show- 

 ing that a greater, portion of the organism has been colored. 

 If, again, such deeply stained preparations are partially decol- 

 orized with acid alcohol, the stain in the wall will be sufficiently 

 removed to demonstrate it as distinct from the central body. 

 This is shown in Fig. 2, E-F. 



The usual method of incorporating upon the cover-glass a 



