ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
195 
results were that B. aceti and B. xylinum are distinguished from B. ran - 
cens and B. pasteurianum by their power of inverting cane-sugar. Malic, 
citric, and hydrochloric acids were found to affect profoundly the shape 
of beer vinegar bacteria. Acetifying bacteria may retain their vitality in 
the absence of air ; and they then reduce indigo-blue, methylen-blue, and 
litmus. The development of these bacteria is always accompanied by 
disengagement of carbonic anhydride. The nutrition of these organisms 
may be divided into genetic nutrition, which determines growth and 
cell-division, and zymotic nutrition, which is not necessarily accompanied 
by growth. The elements indispensable to genetic nutrition are 
C, H, 0, N, K, Mg, and P. Nitrogen may be derived from pepton, 
asparagin, nitrites, or ammonia salts, the carbon from acetic acid, acetate 
of sodium, lactate of lime, and, in the case of B. aceti and B. xylinum , 
from cane-sugar. The assimilation of certain nitrogenised substances 
is determined by the nature of the carbon-nutriment. In addition to 
substances already known, the following may serve for zymotic nutrition : 
lactic, succinic, citric, malic, and gluconic acids, lactate, acetate, and pro- 
pionate of calcium. Tartaric acid is not attacked by acetifying bacteria. 
Quantities of alcohol and of acetic acid compatible with growth have 
no action on the acetifying function. Below 4 per cent, alcohol does not 
influence development, above 4 per cent, it retards it, while near 9 j)er 
cent, there is no longer any development. Acetic acid retards the 
growth, development diminishing in proportion to the increase of acid. 
Species of Acetic Acid Bacteria.* — Herr M. W. Beijerinck recog- 
nises four chief species of acetic acid bacteria : — (1) Bacterium aceti 
Pasteur, the quick acetic acid bacteria ; (2) B. rancens sp. n., beer 
acetic acid bacteria, including cultivated and wild varieties ; (3) B. Pas- 
teurianum Hansen, beer acetic acid bacteria which stain blue with iodo- 
potassic iodide ; (4) B. xylinum Brown, bacteria which are detrimental 
to the acetic acid in vinegar, and form viscid and even cartilage-like 
membranes on saccharated media. Around these four chief species are 
grouped other varieties respecting which more information is promised 
later. 
With regard to B. aceti and B. rancens , the interesting fact is men- 
tioned that the former can derive its nitrogen directly from ammonia 
salt, while the latter cannot. B. aceti forms a vinegar scum on the 
following fluid medium: — alcohol 3 per cent., ammonium phosphate 
0*05, calcium chloride 0*01, tap-water 100. 
Micro-organisms in Flour. f— Mr. C. G. Ferris has examined from 
a bacteriological standpoint numerous samples of flours, and his figures 
show beyond a doubt that the high grade patent flours are much freer 
from bacteria than the medium and common grade products, while the 
number of moulds found in these flours does not vary to the appreciable 
extent that the bacteria do. Seventeen species of bacteria, one yeast, and 
three moulds were found. One bacterium appears to be new. The 
colonies are white, dry, and tough. On removing the growth, a brown 
substratum is revealed. This organism grows readily on agar, wort- 
gelatin, blood-serum, starch and flour pastes. Gelatin is liquefied. The 
* Handelingen 5e« Nederlandsch Natuur- en Geneeskundig Congress, 1897, 
p. 2G3 ; also Centralbl. Bakt. u. Par., 2 te Abt., iv. (1898) pp. 209-16. 
t Proc. Indiana Acad. Sci., 1897, pp. 137-40. 
