VI. The Application of Certain Recent Studies on Technic to 
Methods of Culture of Plant Pathogenes 
Although certain general methods are employed in bacteriology, yet a spe¬ 
cialized technic and special methods of experimentation have been developed 
in each of the several fields of this science variously designated as soil bac¬ 
teriology 7 , dairy bacteriology, hygiene and public health, sanitary engineering, 
medico-bacteriology, pliytopathological bacteriology, etc. Furthermore, the 
methods employed in any one of these closely affiliated fields have been to a 
greater or less degree adapted to meet the needs of investigations in any of the 
others. As regards methods pliytopathological bacteriology, it is believed, can 
with fairness be said to have borrowed from other fields of bacteriology more 
than it has contributed to them. If this assertion be true, it is due largely to 
the fact that this field of study is new and that investigators are not suffi¬ 
ciently familiar with the principles of general chemistry and biochemistry, and 
so are compelled to pursue cultural studies empirically. 
Again, the general bacteriological methods for the study of the biochemical 
activities of bacteria which have been prepared by a committee of the Society 
of American Bacteriologists have come to be more or less standardized and uni¬ 
fied. but, as has been necessitated by fundamental researches, have been modi¬ 
fied from time to time. The present brief consideration is intended only to point 
out some recent improvements and refinements in technic which, it is believed, 
are applicable in cultural studies of bacterial plant parasites, and it is not in¬ 
tended in any way to interfere with the work or prerogatives of the Commit¬ 
tee on the Descriptive Chart, nor in any sense to make suggestions or recom¬ 
mendations to them. No attempt will be made to enter into a comprehensive 
discussion of any of the points, many of which are covered quite fully, either 
in the several foregoing papers or in the work of others to which reference 
has been made in connection with these papers. 
REACTION 
Measurement of acidity. It is to physical chemists that credit is due 
for the development of methods of precision for the measurement of acidity. 
So many reasons have been urged against the employment of titrable acidity 
as determined by Fuller’s scale instead of true acidity or hydrogen ion concen¬ 
tration as may be determined by the colorimetric method with a degree of ac¬ 
curacy sufficient, for bacteriological work that it appears useless to devote 
further space to this subject. If as Clark (1) points out, 1 cc. of N 100 HC1 is 
added to one liter of pure water of pH=7.0 the acidity of the solution be¬ 
comes about pH=5.0. If, however, the same amount of acid is added to beef 
infusion broth of the same initial reaction, the resultant change is hardly ap¬ 
preciable. Equally striking is the observation of Meacham and his associates 
(2) on unbuffed media like corn meal extract in which 2 cc. of normal alkali 
in 1 liter changed the pH from about 4.0 to 10.0. In view of these observations, 
of many others of a similar nature, and of the fact that the Committee of the 
Descriptive Chart (3) has recommended the colorimetric method as more logi¬ 
cal, of more significance, and as simpler, phytopathologists will, in accord with 
other investigators in bacteriology, find no objection to the abandonment of 
the titration method. 
