CLASSIFICATION OF BACTERIA. 



FIG. 



been described by different bacteriologists, but there is great 

 difficulty in giving any distinctive description of such min- 

 ute organisms, which have so few characters, and it is quite 

 uncertain whether these many hundreds of described species 

 represent entirely distinct forms or 

 whether they should be reduced to a 

 much smaller number of species. It is 

 frequently uncertain whether a species 

 described by one bacteriologist is the 

 same as that described by another 

 under the same name. The difficulties 

 which have been found in the .way of a 

 proper description and classification of 

 the species of bacteria have been 

 hitherto insurmountable, and at the 

 present time the subject is in such 

 extreme confusion that no one except 

 an expert can understand it. Fortu- 

 nately, for our purpose this confusion 

 of species is of no importance. We 

 are at present concerned in the results 

 of the action of microorganisms, and 

 only slightly concerned with the prob- 

 lem of the specific characters of bac- 

 teria. All that is necessary for us to know in connection 

 with our subject will be referred to in the separate sections 

 in the following pages, and the subject of the classification of 

 bacteria may be left without further consideration. 



As indicated by this classification, bacteria, although in 

 earlier years frequently called animals, are to-day universally 

 regarded as plants. The reason for calling them plants is 

 not at first sight evident. They are colorless, unlike most 

 plants. They are frequently endowed .with a power of 

 independent motion, a character which would naturally lead 

 to their being called animals. Biologists find it very difficult 



Actinomyces : a, a small 

 co'ony ; b, single rods. (Bos- 

 tram.) 



