6 BACTERIA IN RELATION TO PLANT DISEASES. 
In the present state of our knowledge (1) and (2) can usually be considered 
only after a very careful study of (3), (4), and (5), and of the organism itself. They 
involve a knowledge of modern languages, and a very considerable familiarity with 
scientific literature. 
PREVIOUS LITERATURE. 
One of the first requisites in a student is a knowledge of how to use literature. 
Previous literature is, however, often of such a fragmentary and uncertain sort, as 
we shall see, that it is impossible to decide whether a disease is actually new or has 
been written upon before. 
The literature of plant diseases will not be referred to in this volume, except 
occasionally and incidentally. The bibliography of this volume deals only with 
general bacteriology—human and animal diseases, methods of work, etc. 
*Fic, 3.—A detail from fig. 2. Bacillus carotovorus wedging apart cells of the carrot. Drawn 
mostly from one plane. In placing the cover-glass a few of the bacteria have been crowded out of 
the intercellular spaces into parts they did not originally occupy. X 1,000. 
nN 
