1896.) The Bacterial Diseases of Plants. 639 
containing undetected muscle sugar. Even when preliminary 
tests are made with some gas-producing bacillus there is still 
an opportunity for error, provided the tests are carried on only 
for a day or two. No bouillon should be judged free from 
sugar and safe for use until in fermentation tubes it has been 
subjected for at least a week to the influence of Bacillus cloace 
or some other organism producing an abundance of gas from 
grape sugar. If at the end of this period no gas has developed, 
and the transfer of a loop of fluid from such a tube into an- 
other fermentation tube containing a dextrose-bouillon sets up 
` an evolution of gas, then the first bouillon may be used with 
confidence. Again, if cane sugar is sterilized in an acid 
bouillon at least a part of it is inverted, i. e. changed into dex- 
trose and fructose, and fermentation results obtained therefrom 
may be due to the presence of any one of three sugars. Bouil- 
lon should always be made distinctly alkaline before cane 
sugar isadded. Many of the older fermentation experiments 
are worthless on account of neglect of such precautions, to say 
nothing of some recent ones. Again Bacillus tracheiphilus grows 
not at all or feebly on nutrient gelatine as ordinarily made, or in 
media which is acid beyond a determinable slight degree, and 
if only such media were used the erroneous conclusion might 
be reached that it could not be grown outside of the host plant, 
whereas it grows freely in artificial media, even on gelatine, 
when the right conditions are established. Bacillus amylovorus 
grows well in some gelatines and refuses to grow in others. 
Even comparatively slight changes in the acidity or alkalinity 
of the culture media often have a marked effect on the 
growth of certain organisms, while others, e. g., Bacillus cloacae, 
are able to grow in almost any medium. Many bacteria 
prefer alkaline media, and some are very sensitive to the 
presence of acids, while a variety of bacteria commonly met 
with in water will not develop at all if the medium is rendered 
strongly alkaline. Other organisms grow well in acid media.“ 
14° For a striking illustration of the effect on the growth of water bacteria of 
comparatively slight charges in the reaction of gelatine, see a recent table by 
George W. Fuller, in a paper entitled: (73) On the proper reaction of nutri- 
ent media for bacterial cultivation.—/ournal of the American Public oe 
Lene ams a ‘Concord, as H., Oct., 1895, p. 393. 
