16 TEXT-BOOK OF BACTERIOLOGY. 



is unimpregnable to them, and that is the uninjured, unaltered, 

 healthy organs and juices of the bodies of men and animals. 



This unlimited extent of bacterial life will seem comprehensible 

 by considering- the extremely modest requirements which the low- 

 est representatives of the vegetable kingdom generally make for 

 their development. 



The smallest quantities of organic substance serve for their 

 nourishment; wherever they find these and no particular hindrances 

 to their development, there they grow and multiply. 



It is true they are distinguished from the majority of other 

 plants by their requiring preformed carbonic combinations of or- 

 ganic nature ; that is to say, by their inability to obtain the carbon 

 which they need from carbonic acid pure and simple. They want 

 with the exception of a few species described by Tiegheim the 

 necessary chlorophyl, without the presence of which pure carbonic 

 acid cannot be taken and appropriated for use. 



The plants without leaf-green have been placed together in a 

 group and called "fungi," the bacteria, in consequence of their 

 manner of increasing by division, being called the " splitting fungi," 

 (schizomycetes), as distinguished from the rest, which are called 

 the "sprouting fungi" and the "mould fungi." 



But since there exist, as we have just seen, some bacteria which 

 possess chlorophyl, and since the name " fungi " seems calculated 

 to produce confusion, it is better to renounce it altogether and 

 employ the name " bacteria " for the lowest splitting plants. 



The amount of carbonic acid which the bacteria require in their 

 nourishment, together with the carbonic combinations, may be 

 supplied directly by the organic substance, or by inorganic bodies, 

 such as nitric acid or combinations of ammonia. 



The bacteria, or at least the great majority of them, also re- 

 quire that their food should show an alkaline, or at least a neutral, 

 reaction. On an acid medium most of the bacteria hardly grow 

 at all, whereas the mould fungi, for example, develop successfully 

 upon it. 



An alkaline solution of organic substance is what the bacteria 

 require as a nourishing soil for their development. Nature bounti- 

 fully supplies them with this. Remains of organic matter are every- 

 where to be found, and therefore the conditions for the growth of 

 the micro-organisms are almost universally present. 



Thus a large number of them develop on dead portions of or- 

 ganic origin, remnants of organic life, on remains of dead plants, de- 

 caying corpses in the soil and in the water. 



A comparatively small number, however, are more dainty; they 



