CLASSIFICATION. 25 



bacillus and the diphtheria bacillus are included by some 

 authorities in this class. The streptothrix presents true 

 dichotomous branchings and forms very finely tangled 



FIG. 



Actinomyces. x 250. 



masses. In the course of its growth many stages of the germ 

 are seen. Occasionally the filaments break up and resemble 

 chains of bacilli or cocci, or the free ends of the filaments 

 form club-shaped masses, which may be an evidence either 

 of degeneration or sporulation. 



Depending upon their environment and habits, bacteria 

 are divided into saprophytes and parasites. 



Saprophytes feed only on dead organic matter, and usually 

 are not disease-producing bacteria, unless by absorption of 

 the poisonous products formed by them from the breaking- 

 down proteids. 



Parasites always feed on living organic matter. 



An organism may, however, be both parasitic and sapro- 

 phytic, but a saprophytic existence precludes parasitism. 



According to the results of their vital activity, bacteria 

 are pathogenic and non-pathogenic. 



A pathogenic organism is one which is capable of producing 

 disease. 



A non -pathogenic organism does not of itself produce disease. 



Pure saprophytes are always non-pathogenic germs ; whereas 

 parasites are usually pathogenic. 



The terms obligative and facultative are used to express 

 the absence or presence of the ability of accommodation to 

 surroundings. For example, organisms which may be either 

 saprophytic or parasitic are said to be facultative (typhoid 

 and cholera bacilli). Obligative bacteria are those which 

 must be either one or the other ; as, for instance, the lepra 

 bacillus, which is a strict or obligative parasite. 



