THE VEGETABLE PARASITES. 39 



round, oval, rod-shaped ; straight, wavy, or in the form of 

 a corkscrew. They are never branched, and they multiply 

 by transverse division, which in the rod-shaped forms occurs 

 at right angles to the long axis only, but in the round forms 

 may take place in two directions at right angles to each 

 other. In some of the Bacilli, spore formation has been 

 observed to alternate with multiplication by the above 

 process of fission. This spore formation is sometimes pre- 

 ceded by the growth of the rods into long filaments. The 

 new cells thus formed by fission may separate or may 

 remain united to each other, end to end, forming chains, 

 or lying side by side in more or less spherical colonies, 

 they are frequently bound together by a viscid intercellular 

 matter — zoogloea — formed of mycoprotein or swollen cell- 

 membrane. 



Bacteria multiply at an enormous rate, and Cohn esti- 

 mates that a single organism may give rise to over 16,000,000 

 in twenty-four hours. 



Single round cells have only what is termed the 'Brownian' 

 movement ; but chains and colonies do seem capable of 

 locomotion (Ogsten). The red forms often have a mobile 

 and a motionless stage ; but some, e.g.^ the Bacillus Anthracis, 

 never move. 



CONDITIONS OF LIFE : Food.— Each fungus must be 

 supplied with the materials from which it can extract the 

 elements necessary for growth. These elements, which will 

 vary with each kind of organism, are carbon, hydrogen, 

 nitrogen, sulphur, calcium, potassium, and magnesium. The 

 first four are provided by carbo-hydrates (starchy or saccha- 

 rine compounds) and albuminoids ; the others by inorganic 

 salts. Some Bacteria can assimilate nitrogen and carbon 

 from much less complex bodies than albumen and carbo- 

 hydrates, as is shown by the growth of putrefactive organisms 

 in Cohn's fluid. 



