226 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
water, &c ., which were capable of free development. It was further found 
that such bacteria multiply so much that in about 12 days (at zero) the 
colonies on plate cultivations are innumerable ; this is confirmatory of 
the everyday observation that meat preserved in ice rapidly decomposes 
when thawed. 
A practical outcome of these experiments is that if food-stuffs be 
refrigerated and the air at the same time be dry, they will keep better, 
since the growth of bacteria is materially inhibited by the absence of 
water. 
Osmotic Experiments on Living Bacteria.* — Herr Wladimiroff 
considers that it is not a 'priori improbable that a process similar to 
plasmolysis takes place in the bacterium cell when placed in solutions, 
but believes that the existence of this process cannot be directly deter- 
mined by the Microscope on account of the smallness of the object. 
Observations were therefore made on an easily visible vital process as 
influenced by salt solutions — the mobility of bacteria. This, the author 
believes, stops at the very moment when plasmolysis occurs. Pure 
cultivations of B. Zopfii , Bac. cyanogeneus , Bac. typJii abdominalis, Bac. 
subtilis , Spirillum rubrum, and an intestinal bacterium were placed in 
regularly graduated solutions of the following substances : — KC1, NaCl, 
NH 4 C1, KN0 3 , NaNO Sj NH 4 N0 3 , KBr, NaBr, K 2 S0 4 , Na 2 S0 4 . The two 
solutions, of which in one all trace of movement was extinguished, and 
in the other a trace was just visible, were sought for, and the mean 
between the two was considered to be the plasmolytic boundary solution. 
A great number of substances behaved towards bacteria as might have been 
anticipated from the laws of osmosis — that is, there was a direct relation 
between the action of the solutions and their molecular value. Some 
neutral salts, even in dilute solution, stopped the bacterial movements, 
and this was considered to be the result of a poisonous action rather 
than of plasmolysis. In others the motor palsy first took place under 
much higher degrees of concentration than was expected, and in this 
case it was assumed that the protoplasm was permeable for the substance 
in question. Again, one and the same substance may be permeable for 
one species of bacterium, or another may act plasmolytically, and be 
poisonous to a third. So also very similar substances may have very 
different actions on the same bacterium — e. g. all forms are permeable to 
KC1, and impermeable to NaCl. KN0 3 acts plasmolytically on Bac. 
cyanogeneus , and NaN0 3 poisonously. 
Violet Bacteria, j - — Prof. G. v. Lagerheim noticed on boiled potatoes 
a zoogloea of a deep violet hue, and of very firm consistence. This was 
found to be made up of rodlike bacteria connected together by a copious 
mucus. Experiments to obtain pure cultivations failed. There were 
numerous other bacteria and fungi on the potatoes, and it liquefied 
gelatin without forming violet colonies. Only five other species of 
violet bacteria have been described. 
* Zeitschr. f. Phys. Chemie, vii. (1891) pp. 529-43. See Centralbl. f. Bakteriol. 
u. Parasitenk., xii. (1892) pp. 96-7. 
t Anal. Universidad central del Ecuador, eerie iv. No. 39, 1891. See Bot. 
Centralbl., 1892, Beih., pp. 165-6. 
