14 MORPHOLOGY 



Absolutely unique in the whole of organic creation is the case of those 

 bacteria whose protoplasm contains free sulphur (Chap. VII). In these 

 ' sulphur-bacteria ' the cell is often crammed full of highly refracting 

 globules, which are soluble in alcohol, xylol, bisulphide of carbon, and 

 alkalies, and give other reactions of pure sulphur. It is in a non-crystalline, 

 soft, amorphous state, and when dissolved out by carbon disulphide leaves 

 delicate clear vacuoles in the protoplasm. Deposits of other substances 

 within the bacterial cell have not as yet been observed, with the exception 

 of fat or oil, which sometimes appear in the form of minute globules, 

 particularly in old cultures. 



Movements and Organs of Locomotion. 



All bacteria, whether spontaneously mobile or not, are, when suspended 

 in water, in constant motion. Examined under a high power, they are seen 

 to be shaken by a rapid oscillatory movement. This, the so-called Brownian 

 movement (8), is in no sense a vital phenomenon, but is common to all finely- 

 divided solid particles suspended in liquids. It may be observed in the 

 particles of gamboge or indian ink rubbed up with a little water. Its cause 

 is not well understood. As a general rule there is no danger of mistaking 

 the trembling motion for the spontaneous movements of bacteria. 



There are two kinds of independent motion distinguishable among bac- 

 teria — the ordinary swimming movement, and the rarer ' oscillation ' peculiar 

 to some trichobacteria and similar to the movements of some cyanophyceae. 

 Among the cocci, Micrococcus agilis is the only one endowed with the loco- 

 motory powers, but of the bacilli a large number are actively mobile, such as 

 B. typhi, the butyric bacteria, and the majority of the putrefactive organisms. 

 The vibriones and spirilla, too, are good swimmers. The bacilli of tuber- 

 culosis, diphtheria, anthrax, many of the pigment bacteria, and the acetic 

 and lactic ferments are permanently immobile. When bacteria in active 

 movement are examined under a high power they seem to shoot across the 

 field of view with amazing speed ; but this velocity is only apparent, 

 being due to the magnification of the distances they cover. Reduced to 

 actual figures, the absolute rate of progress is 10 cm. in 15 minutes, or about 

 \ mm. per second — in proportion to their size a very fair speed. 



Locomotion is effected by special organs, the cilia or flagella. In the 

 fresh state, or in bacteria stained in the ordinary way with anilin colours, 

 the cilia are not visible, and special methods of preparation are necessary to 

 render them so. That worked out by Loeffler (9) has the claim to priority and 

 is the best. He employs in the first place a mordant composed of an iron 

 salt and tannin, which causes the stain; to be thrown down not only within 

 the cell, but also upon its surface and upon the surface of the cilia, which 



