32 BACTERIOLOGY. 



organic matters is signally different in different species 

 of bacteria, and, singular to say, there is a small group 

 (to be described later) from which this function is appar- 

 ently absent, in spite of the fact that no compensatory 

 chlorophyll is discernible in their tissues. 



SAPROPHYTES AND PARASITES. In the case of 

 certain bacteria, in fact, the majority, the source of food- 

 supply must of necessity be dead organic matters of either 

 animal or vegetable origin. They cannot exist in the 

 presence of living tissues. To the members of this 

 group the designation sapropJiytic or metatrophic (A. 

 Fischer) is given. To that group that can exist only 

 upon living organic matters, and herein belong many 

 (not all) of the disease-producing bacteria, the appella- 

 tion parasitic or paratrophic (A. Fischer) is applied ; 

 while for the few species that either do not require 

 organic matters, or do not, so far as is known, have the 

 faculty of decomposing and assimilating proteid stuffs 

 at all, the name prototrophic is suggested by Fischer. 

 In the strict sense of the word, a parasite or paratroph 

 can exist only in the body of a living host, and a sapro- 

 phyte or metatroph only upon lifeless organic matters, 

 and such obligate parasites and saphrophytes are known, 

 but in the majority of cases such nutritive conditions are 

 not obligatory, many of both metatroph s and paratroph s 

 having the power to adapt themselves to conditions other 

 than those for which they are by nature best fitted. For 

 instance, certain species that exhibit their most impor- 

 tant properties under conditions of parasitism may, 

 nevertheless, lead a metatrophic existence when circum- 

 stances demand it, and, on the other hand, particular 

 species usually metatrophic by nature may find condi- 

 tions favorable to their development in a living host. 



