46 THE FORMATION OF PROTEIDS IN PLANT-CELLS. 
di-ammonium phosphate.After addition of the organic 
nutrient to be tested, the liquids are inoculated with bacteria. 
In those cases, in which the growth of a specific bacterium has 
to be tested, a previous sterilisation is of course necessary. 
An incipient turbidity, the formation of flocculi or of a thin 
film and the microscopical examination will very soon indicate 
that the bacteria have grown and multiplied. Organic bases 
are best neutralised with phosphoric acid, while acids are best 
applied as sodium salts. 
It is, however, not only of interest to decide, which combina¬ 
tions can serve for nutriment, but also to elucidate the reasons, 
why often closely related compounds behave far differently 
from each other, and why certain substances, which are in 
neutral solution by no means poisonous, cannot be used as 
food. We find for instance that pyridin, pinacon, dimethyloxy- 
pyrimidin, ethylendiamin, amidoacetal, glyoxal, meconic acid, 
oxalic acid in dilutions of 0,5% do not support bacterial growth, 
and acetoxim, diacetonamin, citraconic and maleïc acid permit 
only with difficulty after a series of weeks a gradual develop¬ 
ment. 1 2) These compounds are therefore not well suited for 
the preparation of those atomic groups that serve for the 
formation of proteids. Control experiments with addition of 
0,2% peptone indicated, by the rapid development of bacteria, 
that neither of these substances are poisonous in such a degree 
as to kill the bacteria if well nourished. 
The fact that fumaric acid supports bacterial life so well, 
that a few days after the infection the liquid swarms with 
numberless bacteria, while it takes 4 weeks with the isomeric 
maleïc acid before a slow development, after repeated infection, 
takes place is of biological interest. Whether here a gradual 
adaptation took place or only specific germs were developed, 
remains to be decided. In the case of citraconic acid no 
development for six weeks was observed ; finally, after repeated 
infections a scanty vegetation set in, consisting of apparently 
only one kind of bacterium, forming short thick rods often in 
1) Calcium salts are not necessary for the life and development of the lower 
fungi, Compare O. Loew, On the functions of calcium and magnesium salts in 
plants, Flora 1892. 
2) O. Loew , Centr. f. Bacteriol. 22, 361 
