THE WONDERS OF LIFE 



plasma-granule, we can only distinguish three funda- 

 mental types: (i) Micrococci, or spherobacteria (briefly, 

 cocci), globular or ellipsoid; (2) bacilli, or rhabdo-bac- 

 teria (also called eubacteria, or bacteria in the narrower 

 sense), rod-shaped, cylindrical, and often twisted like 

 worms (comma-bacilli) ; (3) spirilla, or spirobacteria, 

 screw-shaped rods (vibriones when the screw is slight, 

 and spirochaeta when it has many coils). Besides this 

 threefold difference in the forms of the cytodes, we 

 have a ground of distinction in many bacilli and spirilla 

 in the possession of one or more very thin lashes (fla- 

 gella), which proceed from one of both poles of the 

 lengthened plastid. The construction and vibration of 

 these serves for locomotion in the swimming bacteria; 

 but they are only found for a time in many species, and 

 in many others are altogether wanting. 



Since, then, neither the simple outer form of the 

 bacterium - cytodes nor their homogeneous internal 

 structure provides a satisfactory ground for the sys- 

 tematic distinction of the numerous species, their physio- 

 logical properties are generally used for the purpose, 

 especially their different behavior towards organic foods 

 (albumin, gelatine, etc.), their chemical actions, and the 

 various effects of poisoning and decomposition which 

 they produce in the living organism. No bacteriologist 

 now doubts that all the vital activities of the bacteria 

 are of a chemical nature, and precisely on this account 

 these microbes are of extreme importance. When we 

 bear in mind how complicated are the relations of the 

 various species of bacteria to the tissues of the human 

 body, in which they cause the diseases of typhus, hypo- 

 chondriasis, cholera, and tuberculosis, we are bound to 

 admit that the real cause of these maladies must be 

 sought in the peculiar molecular structure of the bac- 

 terium-plasm, or the particular arrangement of its mole- 

 cules and the innumerable atoms (more than a thousand) 



202 



