In the following table are recorded more in detail the results obtained by Kraus on introducing cholera bacilli into three different unsterilised waters at Munich :

Cholera Bacillus

:

In connection with the vitality of the cholera bacillus in water, some recent investigations made by Trenkmann1 are of considerable interest. In these researches varying doses of different salts were added to a particular well-water kept at from 21°-24° C.; the cholera bacillus was introduced, and its subsequent behaviour carefully watched by means of plate-cul

In some experiments the water was sterilised, whilst in others it was used in its natural condition, and the competition between the ordinary water bacteria with the cholera bacilli was noted.

One, two, or three drops, as the case might be, of a 10-per-cent. solution of sodium chloride, sodium nitrite, sodium nitrate, sodium carbonate, disodium phosphate, also potassium chloride, potassium nitrate, sodium sulphide, were added to 10 c.c. of the water contained in test-tubes.

These salts were selected as being those which might normally be present in waters of different kinds, although even the lowest proportions in which they

1Beitrag zur Biologie des Kommabacillus,' Centralblatt für Bakteriologie, vol. xiii., 1893, p. 313.

were added by Trenkmann exceeds that generally present in ordinary drinking waters.

Again, in the inoculation of the cholera organism considerable quantities of organic material must also have been introduced into the waters, for the bacilli were abstracted direct from broth-cultures by means of a needle-loop, in which manner, of course, an appreciable amount of broth was also introduced, and the character of the water materially altered. This error is one, as we have already pointed out, which has been unfortunately made by many investigators, and has greatly detracted from the value of the results obtained.

The following table may be cited as an example of the mode of investigation pursued, and of the results obtained :

On the control-plate, poured immediately after the introduction of the bacilli, there were (1,440) colonies of cholera bacilli. 1,880

25-27 drops=1 c.c.

It is much to be regretted that this investigator has departed from the time-honoured custom of determining the number of bacteria in 1 cubic centimetre, and has substituted for this the irrational and ephemeral unit of volume represented by the drop of liquid contained in a particular needle-loop in his possession.

From these experiments it appears that in those waters to which no additions of salt had been made the cholera bacilli rapidly diminished in numbers, whilst in the others their multiplication took place almost in proportion to the quantity of salt added, this being especially marked in the case of No. 17.

It was also found that the addition of potassium salts stimulated the vitality of this bacillus in a marked degree, three drops of a 10-per-cent. solution of potassium chloride inducing an increase in the numbers present after twenty-four hours from 1,020 to 43,320 in the needle-loop.

Experiments were also made with unsterile water, as will be seen from the following table :

The author has unfortunately omitted to state the number of cholera bacilli introduced into this water, but from his remarks it would appear that the initial number must have been largely in excess of 216 per needle-loop.

Thus in the unsterile water the cholera bacilli quickly diminish, whilst the water bacteria rapidly multiply. The addition of sodium chloride markedly stimulates the vitality of the water bacteria, so much so that when only one drop was added the cholera