The official salt employed is silver nitrate, a crystalline salt which is decomposed by oxidizable organic matter and light, and is soluble in less than its own weight of water. "Lunar caustic" is silver nitrate toughened by the addition of hydrochloric acid to make a small amount of silver chloride (horn silver), and molded into sticks.

Silver nitrate is antiseptic and very irritant locally. It coagulates protein, so is astringent, and may readily destroy the soft tissues, so is caustic. It has little penetrating power, and its action may be checked very promptly by sodium chloride, which changes it to the inert silver chloride. Wildbolz (1907), by reduction with the Finsen light, found that 1: 1000 to 1: 100 solutions penetrated to the subepithelial tissue of a dog's urethra, while 1 to 3 per cent. solutions of protargol had less penetrating power.

In 2 per cent. solution silver nitrate is used as a prophylactic against gonorrheal ophthalmia in the newborn (Crede's method). In 0.5 to 5 per cent. solution it is employed in nose and throat, or for cracked nipples or canker sores or ulcers, and in 0.1 to 1 per cent. solution for the conjunctiva, vagina, urethra, bladder, or rectum in various infections.

The lunar caustic is employed to destroy exuberant granulations, to remove small neoplasms, warts, condylomata, etc., and to stimulate the surface of a sluggish ulcer or sore. To remove a wart the pointed caustic stick is moistened and bored down into the central artery of the wart. The wart turns black and may be removed in a few days.

In the stomach, the nitrate has been employed in hyper-chlorhydria and chronic gastritis; but as it is immediately rendered inert by hydrochloric acid or sodium chloride, it is useless unless preceded by thorough lavage. If it is employed at all, the best method is to administer it in 1: 500 solution through the lavage tube, and then, after two or three minutes, to remove it by thorough lavage. If it is desired to give silver nitrate in pills, kaolin and petrolatum should be employed in their manufacture, for extracts, glucose, glycerin, and other organic excipients will render the nitrate inert.

In the bowel, it has much local employment in colitis and proctitis. Rogers found that in aqueous solution 1: 10,000 killed the dysentery bacillus in five minutes, but that in the presence of organic matter and salts it failed to kill in a strength of 1: 100. Not infrequently it increases the irritation instead of curing it.

The nitrate makes a black stain on exposure to light, to remove which the skin may be washed with solution of potassium cyanide, or covered with tincture of iodine and washed off with solution of sodium hyposulphite.

A number of organic silver compounds are also to be had, the most used of which are argyrol (silver vitellin) and protargol (silver protein). Colloidal silver, collargol, is also employed by mouth in dose of 45 grains (3 gm.), by inunction with a 15 per cent. ointment, and intravenously for septic conditions in doses-of 2 drams (8 c.c.) of a 2 per cent. solution. Dunger has shown that an intravenous of collargol suspension caused a prompt destruction of 40 to 80 per cent. of the circulating leucocytes. but stimulated the bone-marrow so that in twelve hours the leucocyte count was restored. These preparations are not essentially astringent, and are not precipitated by albumin and chlorides. As argyrol and collargol are non-irritant, and protargol only slightly irritant, they have come into very extensive use to replace silver nitrate. Comparative studies of the relative antiseptic values of the silver preparations show that the only one with pronounced germicidal effect in aqueous solution is the silver nitrate; but that albuminous substances, as in serum and the tissues, quickly destroy its antiseptic power. In Rogers experiments with the dysentery bacillus, albargin (silver gela-tose) gave the best results in the presence of organic matter and salts. Marshall and Neave have shown that the percentage of silver does not indicate the antiseptic value.

Derby (1906) tested a staphylococcus on a mixture of hydrocele fluid and bovine serum. With an equal volume of 2 per cent. silver nitrate he could still obtain a growth after thirty to forty minutes; with an equal volume of 8 per cent. protargol, a growth after sixty minutes; and with 50 per cent. argyrol, an abundant growth after three and one-half hours.

Bayard Clark and Wylie (1911) report an extensive series of comparative bacteriologic studies, from which we take the following as examples:

Organism

Solution

Number of Colonies from One loopful taken after

5 minutes

15 minutes

30 minutes

Streptococcus...

2 per cent. silver nitrate. .....

0

0

0

1 per cent. silver nitrate. .....

6

5

0

10 per cent. protargol.....

25

20

20

30 per cent. argyrol ............

0

0

0

10 per cent. argyrol...................

4

0

0

2.5 per cent. collargol.............

15

8

0

Gonococcus.....

1: 5000 silver nitrate.....

0

0

0

1: 1000 silver nitrate.....

0

0

0

10 per cent. protargol.....

30

25

15

30 per cent. argyrol ...............

70

50

10

2.5 per cent. collargol ............

80

100

15

These might be compared with the table given under Disinfectants, page 490.

Untoward effects of silver are: (1) argyria, a bluish staining of the skin which is permanent. It may appear in spots (the "spotted boy" of the circus). It usually was the result of the now obsolete treatment of epilepsy and other nervous diseases with silver nitrate. It is reported from the use of collargol.

(2) There is also at times from the local use in the eye a conjunctival argyria. According to Theobold, this is more common from the organic compounds than from the nitrate.

Collargol and argyrol solutions are employed for injection into the ureters to obtain x-ray pictures of the ureter and kidney pelvis.