Klein' has studied systematically both the disinfectant and antiseptic action of perchloride of mercury when applied in the form of a solution in distilled water. Various bacteria were added to such solutions of different strengths and kept therein for a variable length of time; afterwards the vitality of the organism. was tested in the usual fashion. The modus operandi was as follows: Into a freshly drawn out glass pipette a droplet was drawn up of the bacterial fluid, and into the same pipette the mercurial solution was drawn up in such a way that the original bacterial droplet was diluted by the mercurial solution 100 times. After leaving the bacterium and the disinfectant thus in apposition for a given time, samples of the mixture were used for inoculation of culture tubes containing solid nutritive gelatin or fluid media (generally sterile faintly alkaline broth peptone 1 per cent.) or 1 per cent. meat extract peptone. These tubes were then placed in the incubator, and the growth occurring in them if any, its character, and its differences from those of the normal organism noted.

The bacillus subtilis, in the spore state, was not killed in a less dilution than 1 per cent; the sporeless bacillus subtilis was killed in solutions of a strength of from 1: 10,000; and from 1: 15,000. As regards the restraining or antiseptic power of corrosive sublimate on the growth of the bacillus subtilis, it was found that one part of sublimate added to 10,000 of gelatin prevented growth. Very similar, almost identical results were obtained with Finkler's comma bacillus and the comma bacillus of Koch.

Micrococcus prodigiosis was somewhat easier killed than the foregoing, the restraining power of medicated gelatin was the

same.

Anthrax.-Spores are only killed in solutions of sublimate 1 per cent. and above. Klein thus sums up the results of his numerous experiments on the antisepsis of anthrax spores :-Sublimate in nutritive gelatin in the proportion of 1 in 10,000 does not always prevent anthrax spores from germinating and producing there a crop of bacilli; but in those cases in which such amount of sublimate failed to inhibit their germination and growth, the salt had nevertheless a certain restraining influence

1 Supplement, Fifteenth Annual Report of the Medical Officer to the Local Government Board, 1885, p. 155.

since the growth was retarded, was very small in amount, and its infective power was diminished, and moreover this diminution of infectivity increased with time until its total extinction was achieved. But gelatin sublimate 1 in 50,000, and in lesser proportion, has no restraining power. Sporeless bacilli are killed when treated with solutions of sublimate 1: 2,000. One part of sublimate added to 2,000, 3,000, or 4,000 of gelatin inhibit growth as a rule; in solutions of sublimate of 1: 5,000, the bacillus grows, but in some cases its infective properties are remarkably modified.

The Bacillus Septicemia of Guinea Pigs.-Sublimate solutions of 110,000 kill both spores and threads when acting for thirty minutes. One part of sublimate in 10,000 of gelatin inhibit growth.

Tubercular virus experiments made by Lingard show that a solution of sublimate, strength 1: 960, destroys in from four to eight hours human tubercular virus; the exposure requires to be longer in the case of bovine tubercular virus.

THE HALOGENS.

(254) Chlorine, at. weight 354, a yellowish green Gas, 2.4 times heavier than Air.

It may be prepared for the purposes of disinfection by heating together a mixture of common salt, manganese binoxide, and sulphuric acid, the following reaction occurring: 2 NaCl + MnO2 + 2H, SO1 = Cl2+ Na2 SO + MnSO4 + 2H2O, or simply by the action of hydrochloric acid on manganese binoxide, MnO2 + 4 HCl = MnCl2 + Cl2 + 2H2O, but both these processes are somewhat inconvenient, and it is in practice almost invariably evolved from bleaching powder by the addition of an acid.

Bleaching powder may be considered to have the formula CaCl,O2+ (CaCl, CaO) 2 H2O, that is, to be a mixture of hypochlorite and oxychloride of calcium, although its composition is much disputed. Theoretically it should contain 41 per cent. of chlorine, but in practice it is seldom that more than 35 per cent. can be obtained. 1 lb. of good bleaching powder on being

treated with sufficient acid to completely decompose it, will evolve about 18 cubic foot of chlorine gas. To obtain anything approaching the percentages that Fischer and Proskauer found most efficacious, 2 lbs. of bleaching powder decomposed by 3 lbs. of strong hydrochloric acid will be necessary for every 1,000 cubic feet of space; this is of course on the assumption that chlorine gas will alone be used, but if as recommended at page 359 the disinfection be a combined operation, that is fumigation, heat, and afterwards mechanical processes of cleansing, then a less quantity suffices, and in practice 1 lb. of bleaching powder to 1,000 cubic feet of space will be ample.

(255) Iodine, at. weight 1265, density 126 5. Iodine forms rhomboidal lustrous greyish black plates. Iodine dissolves but sparingly in water, but its solubility is much increased by certain salts, e.g., potassic iodide; it dissolves freely in alcohol, in ether, and in carbon disulphide. It is not well adapted for use as a fumigating agent chiefly on account of the density of its vapour which is 85 times heavier than air; hence it is extremely difficult to diffuse it properly.

(256) Bromine, at. weight 798, density 79.8.

Bromine is a dark red liquid of an exceedingly irritating odour. It is soluble in water, a saturated solution containing about 3 per cent. at ordinary temperatures. A method of using it as a fumigating agent is given at page 344.

(257) The Experiments of Cash on the Halogens.

The most important experimental determination of the value of the halogens has been made by Dr. Cash, F.R.S. (Supplement to the Sixteenth Annual Report to the Local Government Board.) The object of the inquiry was to determine the lethal limits of chlorine, iodine, and bromine, as well as sulphurous acid, to anthrax, to human and bovine tuberculosis.

Dr. Cash thus describes the methods he adopted :With the object of rendering the investigation as precise as possible, I have when testing the effect of solutions of these

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halogens, employed graduated strengths which could be readily controlled by means of occasional standardizing.

Water solutions of chlorine lose strength with more or less rapidity, solutions of sulphurous acid rapidly, a partial conversion into sulphuric acid as a result of oxidation taking place. Bromine in solution is moderately stable, and iodine practically perfectly so.

Using a solution of iodine of known strength as the starting point for the standardizing of the other solutions, and taking of it an solution (i.e. 12.653 grms. of iodine per 1,000 c.c. distilled water, or 1.27 per cent), it is easy to satisfy ourselves that an equal volume of standard hyposulphite solution discharges the colour of the iodine, starch being used as the indicator. The hyposulphite being found up to strength, the standardizing of the chlorine and bromine solutions is effected by estimating their power liberating iodine from iodide of potassium, starch as before being used as indicator.

of

Koch places the solutions of the halogens which arrest the development of anthrax bacillus as follows:

Iodine 1: 5,000, Bromine 1: 1,500, Chlorine 1: 1,500.

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He farther found that spores of anthrax were destroyed in iodine (1: 7,000) one day; bromine (two per cent) one to five days; chlorine (freshly made) one to five days. The original solutions employed were of iodine, of bromine, of chlorine From these more dilute solutions were made by careful measurement and controlled by standardization the solutions having the following values-iodine 1.27 grms. in 1,000 c.c. of water: chlorine 3537 in 1,000 c.c. water; bromine 7975 in 1,000 c.c. water.

The real question at issue is not merely the action of a certain solution having a given percentage strength, but the action of such a fraction, say of a cubic centimetre containing a known. quantity of the disinfectant upon a given quantity of blood or cultivating medium within which the particular micro-organism is present.

Supposing, for instance, that we expose one twentieth of a drop of anthrax blood to the action of iodine, we obtain no definite notion of its disinfecting power by stating that the latter was present in the proportion of one per cent. in the solution unless we know farther the actual quantity of the solution available for action upon the micro-organisms. By exposure in a hermetically

sealed bulbous pipette the strength of the solution is well insured during its action, its complete mixture having been accomplished beforehand in a watch glass.

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Supposing, to complete the example, that 1 c.c. of iodine solution is mixed with one twentieth drop of anthrax blood, we then have as iodine actually present, in 1 c.c. 00127 and one tenth c.c. = 000127 grm. We can state therefore that this quantity of iodine acting for five minutes upon one twentieth drop of anthrax blood destroys the contained bacilli, in other words thoroughly disinfects it in a given time.

The experiments hitherto made with the haloid bodies and sulphurous acid are in so far double, as they test the disinfectant action of these bodies in solution and as vapours passed through a solution containing the micro-organism to be disinfected.

In the end it is true that the effect is-as the menstruum becomes more and more highly charged with gas which is dissolved in it-in both cases that of the exposure of a cultivation of whatever the microbe may be to a disinfectant solution; but it is in the first instance a matter of considerable interest and utility to determine how far the passage of gas through an infusion of some pathogene will destroy its life, when, by reason of the speed of its transmission probably not all but a part only of the gas acts directly upon it. It is in the first instance less a question of the action of a saturated fluid than it is of the affinity of the passing gas, so to speak, for the microbe with which it is in conflict. Even at very low speeds of delivery of air charged with disinfectant vapour, of say, 12 to 20 bubbles per minute, it is found that from the first a certain amount of gas, be it chlorine, bromine, or SO2, passes through the infusion of the pathogene and discharges iodine on the distal side from an iodide of potassium solution. If, on the other hand, a substance such as KI, upon which the generated gas acts chemically, liberating iodine, be substituted for the pathogenic infusion so that we have two vessels containing KI solution in series, we find that a very rapid discharge of the gas is necessary to decolourize the solution situated distally; not until all the KI is decomposed in the vessel into which the gas first passes, does the farther vessel begin to show decolourization likewise.

Experiments were made with solutions of the halogens and also on infusions of virus traversed by the gas.