It is advantageous to add a little more iodide if hard water is used instead of distilled water; and in any case an excess of the iodide can do no harm. If no biniodide is at hand, a lotion can easily be made by taking a 1 in 1000 solution of sublimate and adding iodide of potassium or of sodium to it. At first the red iodide is precipitated, but this is quickly dissolved by the iodide, and a clear watery solution is the result. But it would be an error to suppose that the result would be a 1 in 1000 of biniodide of mercury solution. As a matter of fact, as Mr. F. R. Jones has recently pointed out, it is nearly twice as strong, being approximately 1 part of biniodide in 600 parts of water. When sublimate is used for making biniodide of mercury lotion and a 1 in 1000 solution is required, it is only necessary to use 6 grs. of sublimate and 6 grs. of iodide of potassium or of sodium to the pint of distilled water. For private practice the small soloids of biniodide are useful. It is important to see that these are made of a convenient size, so that one soloid makes, say, a pint of lotion, the strength of which is 1 in 1000. Also the soloids ought to dissolve at once in tepid water.

I now use biniodide throughout the operation for rinsing out the sponges, for the occasional flushing of 1 Brit. Med. Journ., London, Oct. 18, 1898.

ΙΟ

the wound, and for the continuous bathing of the hands of the operator and of his assistant. All of these have, of course, been previously disinfected in the way I shall describe, and the biniodide is used as an antiseptic. For this purpose it is most efficient. A solution of 1 part in 500 parts of rectified or methylated spirit is used to disinfect the skin.

CHAPTER XIII.

CARBOLIC ACID.

EXPERIMENTERS seem to make the most contradictory statements concerning phenol or carbolic acid. According to Evans,1 a 2 per cent. solution of carbolic acid is said by one observer to kill Staphylococcus aureus in eight seconds, whilst another asserts that this is only achieved after fifteen minutes. Evans' own results are almost the same, for he found that 1 in 40 took fifteen minutes to kill aureus in broth.

Mr.

Carbolic acid came badly out of Geppert's tests. Anthrax spores, after lying for thirty-eight days in a 7 per cent. solution, grew on agar-agar, and killed guinea-pigs.2

3

Christmas says anthrax spores may be kept in 20 per cent. carbolic acid for a month without the least

1 Guy's Hosp. Rep., London, 1890, vol. xlvii. p. 245.

2 "Ueber Desinficirende Mittel und Methoden," Berl. klin. Wchnschr., 1890, S. 247.

3 Loc. cit., p. 276.

alteration.

Even 50 per cent. carbolic took eight

days to kill anthrax spores.

In Klein's experiments mature anthrax bacilli were killed in five minutes by 5 per cent. carbolic lotion.1

Gärtner and Flügge2 seem to have obtained the same exceptionally favourable results with carbolic acid as they did with sublimate. They claim that a 3 per cent. solution killed non-spore-bearing anthrax and a variety of pyogenic cocci and streptococci in eight seconds. But Vinay found that anthrax spores were alive after soaking for thirty-seven days in 5 per cent. carbolic lotion. Klein says the spores are "stunned," not killed, by the carbolic, because when they are taken out of it and put into animals they recover and cause death. The effects of carbolic acid upon the typhoid bacillus is also very slight. It grows well in the presence of considerable quantities (4 per cent.). Indeed, this peculiarity is used to separate the typhoid bacillus from other kinds.

3

Schill and Fischer say that sputum containing tubercle bacilli and their spores is disinfected by an equal volume of 5 per cent. carbolic lotion in twenty-four hours. A 1 in 500 solution of sublimate

1 Quoted by Rideal, loc. cit., p. 151.

2 Flügge, loc. cit., p. 668.

3 Quoted in article on "Disinfection," Quain's "Dictionary of Medicine," 1894, p. 525.

was not efficient in the same time and in the same quantity. I have already pointed out that disinfection depends both upon the chemical which is used and upon the microbe which is acted upon by it, as well as the conditions under which the chemical acts.

Carbolic acid kills spores much more quickly when it is mixed with hydrochloric acid. In this respect it resembles sublimate. A 1 per cent. solution of carbolic acid in water took thirty days to destroy anthrax spores. A 1 per cent. solution of hydrochloric acid took as long. A mixed solution of 2 per cent. carbolic acid and 1 per cent. of hydrochloric acid killed the spores in seven days; 4 per cent. of carbolic acid and 2 of hydrochloric acid destroyed spores in less than an hour. The carbolic acid alone required at least twelve days.1

Chamberland and Roux 2 found that 。 of carbolic acid prevented the formation of anthrax spores in broth. Anthrax grown in the presence of carbolic acid was permanently attenuated. This is a most important observation.

Dr. W. Black Jones tested the relative disinfecting properties of sublimate, biniodide of mercury, and of

2 On the Attenuation of the Bacterium of Anthrax by the Influence of Antiseptic Substances, "Microparasites in Disease," New Syd. Soc. Translation, p. 604.