invalidate the present methods of sterilization for operations. They naturally stimulate interest in the discovery of better methods of sterilization and especially in the thorough application of the methods upon which we are now depending, in order to obtain the best possible results from them. There are three ways of destroying microorganisms: (1) by deprivation of food and water, (2) by chemicals (including toxins), (3) by heat.

Chemical Antiseptics. For practical disinfection, chemicals and heat need only concern us. The power of these substances is greatly decreased by heat, grease, oil, mucus, and even blood will cover germs with a coating which prevents chemical germicides from reaching them. Among the ordinary germicides, bichloride of mercury, iodin, alcohol and carbolic acid, are of the greatest importance. A source of error in the direct application of these experiments is the fact that many of these chemicals are decomposed or rendered inert, by combinations with the albuminoids of blood and pus, mercuric bichloride being transformed into an indifferent substance and even carbolic acid being altered.

Carbolic Acid is a valuable germicide in the strength of from 1 to 40, to 1 to 20. It is very irritant to tissues and carbolized dressings may be responsible for the sloughing of a wound. It is inert in fatty tissues.

Carbolic acid is readily absorbed, and may thus produce toxic symptoms. One of the early signs of absorption is the appearance of the urine, which may assume a smoky, greenish or blackish hue. Examination shows a great diminution or entire absence of sulphates, when the acidulated urine is heated with chloride of barium. The urine also contains albumin. The appearance of the urine is an indication that the use of the drug must be discontinued.

Kreolin, a preparation made from coal tar, is a germicide without irritant or toxic effects. It is less powerful than carbolic acid, but acts similarly, and is used in emulsion of a strength of from 1 to 15%. It does not irritate the skin like carbolic acid.

Peroxide of Hydrogen is a most admirable agent for the destruction of pus cocci. It probably destroys the albuminous element upon which the bacteria live, and starves the fungi.

Peroxide is not fatal to tetanus bacilli.

Iodoform is largely used, but it is not a germicide as bacteria will grow upon it. It hinders the development of bacteria and directly antagonizes the toxic products of germ life.

Silver Nitrate is a valuable antiseptic. It exerts an inhibitive action upon the growth of microorganisms, but irritates the tissues.

Formaldehyde has valuable antiseptic properties. Formalin is a 40% solution of the gas in water. Solutions of this strength are very irritant to the tissues, but a 2% solution can be used to disinfect wounds and instruments.

Nucleins, especially protonuclein, possess germicidal powers. Protonuclein is of value in treating areas of infection, particularly when sloughing exists. A great many other antiseptics are used.

Heat. The surest and quickest method of destroying bacteria is by heat. Even the spores succumb to it. Anthrax spores are killed in 2 minutes in boiling water, and the various bacilli and cocci in from 2 to 5 seconds.

When a substance to be sterilized by heat will not bear so high a temperature, the method of fractional sterilization is employed, the fluid to be sterilized being heated to from 140°F. to 175°F. or to from 69°C. to 80°C., for from 15 to 30 minutes every 3 days or 7 days. The theory is that the adult germs are killed by the first heating and that any spores which develop subsequently are destroyed in their adult state at the next heating. The fluid, meanwhile, must be kept at an even temperature which will encourage the development of any spores it may contain. Even anthrax spores may be killed by 167°F. to 185°F., or 75°C. to 80°C., in a one and four-tenths solution of bicarbonate of soda, in from 8 to 20 minutes. Dry heat is not so efficient as moist heat.

The following are the more important bacteria we meet in surgical conditions:

The first six are known as pyogenic bacteria, as they all produce pus; in addition to the above there are many more microorganisms, but from a surgical standpoint those mentioned are the most important.

The staphylococcus pyogenes is a spherical coccus of somewhat variable size but averaging about 8 microns; when properly stained it can often be seen to be formed of two separate hemispheres. In pus it is generally found in small heaps containing from two to ten members, but it also occurs singly and in pairs, and even in short chains like the streptococcus, thus rendering diagnosis difficult with the microscope alone. Its cultures are of a yellowish tinge. The aureus type is the most usual cause of abscesses (circumscribed suppurations) and 77% of acute abscesses are due to the staphylococci.

The staphylococcus pyogenes aureus is a facultative anaerobic parasite which is widely distributed in nature, and is found in the soil, in the dust of air, in water, in the alimentary canal, under the nails, and in the superficial layers of the skin. It forms the characteristic color only when it grows in air. It is killed in ten minutes by a moist temperature of 58°C. and is instantly killed by boiling water. Carbolic acid (1 to 40) and bichloride of mercury (1 to 2000) are quickly fatal to these cocci.

Staphylococcus pyogenes citreus, the lemon-colored coccus, is found occasionally in acute circumscribed suppurations, but far more rarely than the other two forms. Its pyogenic power is even weaker than that of the albus.

Staphylococcus pyogenes albus, the white coccus, acts like the aureus, but is more feeble in power. When this organism is found upon and in the skin, it is called staphylococcus epidermis albus, an organism which is the cause of stitch abscesses.

Streptococcus pyogenes is found in spreading suppurations and in very acute abscesses. About 16% of acute abscesses contain streptococci. It is easily killed by boiling, and can be destroyed by carbolic acid and by corrosive sublimate. The streptococcus of erysipelas is thought to be identical with the streptococcus pyogenes, but their difference in action is believed to be due to difference in virulence induced by external conditions and by the state of the tissues of the host. The coccus of erysipelas is larger than the ordinary form of streptococcus pyogenes, and infection takes place through a wound, often a very trivial one, or through a mucous membrane. The organism multiplies in the small lymph channels. The streptococcus may cause suppuration in erysipelas, mixed infection not being necessary to cause pus to form.

The gonococcus of Neisser is found both inside and outside