32 BAGTEBIOLOOY. 



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. 



In the case of certain bacteria, in fact the majority, 

 the source of food-supply must of necessity be dead 

 organic matters, be those of animal or vegetable origin. 

 They cannot exist in the presence of living tissues. To 

 the members of this group the designation saprophytio 

 or metatrophiG (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, tlie appellation parasitic or paratrophio (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 proto- 

 trophic 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 saprophyte or metatroph 

 only upon lifeless organic matters, and such obligate 

 parasites and saprophytes are known ; but in the major- 

 ity of cases such nutritive conditions are not obligatory, 

 many of both metatrophs and paratrophs having the 

 power to adapt themselves to conditions other than 

 those for whicJi they are by nature best fitted ; thus, 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. 



