box with double walls on sides, top, and bottom, provided with tightly-closing doors on one side. The space between the walls is about two inches wide and is filled with water. Heat is applied by a sufficient number of gas-flames, placed beneath, to raise the temperature to 85° or 95° C. The interior is fitted with shelves, upon which are placed in a slanting position the test-tubes containing the blood-serum to be coagulated. In the top are openings for thermometers, for the introduction of water, etc. Good dimensions are 20 X 14 X 14 inches, outside measurements. In using the apparatus time may be saved in heating the water by filling the water-jacket with hot water from a hot-water tap. To facilitate the removal of the water a small faucet should be let into the outer wall near the bottom.

Gas-stove. This is used for boiling culture-media and in the cleansing of test-tubes. It may also be used to heat the "blood-serum coagulator." The stove should have a radial burner which gives a steady blue flame.

Test-tubes.-The most convenient size is 1.80 X 16 cm., or 6X in.

Hypodermic Syringes.-The most useful and durable have an asbestos packing and a glass barrel prolonged into a nipple with a ground surface, upon which the needle fits by means of a cap. These can be sterilized by steam without impairment of their efficiency.

Cornet cover-glass forceps (Fig. 13) should be so con

FIG. 13.-Cornet's cover-glass staining forceps.

structed that the jaws close at an angle between 90° and 180°. This prevents the annoying draining off of the staining solution from the coverglass.

Dropping-bottles (Fig. 14).-These are very useful for holding the staining solutions. The form known as the “T. K. patent" is the best.

The "platinum wire" or "loop" consists of a piece of platinum wire of about 22 gauge, 21⁄2 to 3 inches long, fixed in the end of a small glass or metal rod 8 or 10 inches long. It is often of great convenience to have two of these instruments, one with the wire curled into a simple loop about 1 to 2 mm. in diameter at the free end, and the other a straight wire with the free extremity hammered flat into a very small spatula. The latter is of great utility in picking up minute portions of bacterial colonies.

FIG. 14.-Droppingbottle.

For cultures from tissues a stouter platinum wire, mounted on a metal rod, is desirable. The wire should be about 21 inches long, of a thickness of about 1.2 mm., and should have its free extremity flattened so as to form a small spatula, as in the case of one of the thinner wires above mentioned.

Bacterial Filtering Apparatus.-Various forms of this apparatus can be obtained from the dealers. In all, the fluid from which the bacteria are to be removed is drawn through an unglazed porcelain cylinder into a receiving flask by means of a vacuum-pump attached to a water-faucet which exhausts the air in the receiving flask. It is usually well to connect a Woulff bottle or a vacuum-flask between the pump and the receiving flask, to intercept any water which may come from the pump.

For filtration of small quantities the apparatus known as the Kitasato filter (Fig. 15) is perhaps as satisfactory as any. Before using, the entire apparatus should be sterilized for half an hour in the steam sterilizer.

Wire Baskets. These are used for holding test-tubes during the process of sterilization. They are very cheaply made out of a moderately stout galvanized-iron wire netting of to inch mesh. They should be of two formsviz. round and square. The round form should be of sufficient diameter to fit easily into the Arnold steam sterilizer.

The square form should be made to fit the hot-air sterilizer. Each form should be 10 or 12 inches deep.

Tin Cups.-These are used for holding test-tube cultures upright in the thermostat. In the bottom of each cup a layer of cotton should be placed to prevent the breaking of the tubes.

Thermo-regulator (Fig. 16).—The simple form known as the "Reichert" is recommended.

II. CULTURE-MEDIA.

CULTURE-MEDIA consist of various nutritive substances, either liquid or solid, in or upon which bacteria will grow and multiply, and are, as a rule, contained in test-tubes ready for use.

The nutritive material in these test-tubes must be free from

living bacteria-i. e. "sterile "-and must be kept so until used. This is accomplished by inserting a stopper of raw cotton into the mouth of each test-tube to exclude the entrance of bacteria from without, and then subjecting the tubes and their contents to the sterilizing action of live steam for the purpose of killing any bacteria which may have gained access to the medium during its preparation. The Preparation of Test-tubes.-New test-tubes should be washed in a very dilute solution of nitric acid (2-5 c.c. of the commercial nitric acid to the liter of water), then thoroughly rinsed in water and allowed to drain until dry or nearly so. The object of the use of the nitric acid is to remove any free alkali which may be present in the new tubes.

Old test-tubes containing culture-media, after removal of the cotton stoppers, should be boiled for from half an hour to one hour in a solution of common soda (4-6 per cent.). This treatment not only destroys bacteria, but it also loosens and liquefies the material in the tubes, so that it may be easily removed with the aid of a test-tube brush and plenty of water.

When all the material has been removed from the testtubes in this way, they are to be rinsed in clean water, then in the dilute nitric acid of the strength above indicated for the new test-tubes, and finally again rinsed in clean water, after which they are to be allowed to drain until dry or nearly so.

The test-tubes thus prepared are next to be provided with stoppers of raw cotton (not absorbent cotton), which are to be inserted into the mouths of the tubes for a distance of about 3 cm., and should fit the walls of the tubes smoothly. The stoppers should not be packed in nor fit too tightly, but be just firm enough in position to easily sustain the weight of the tube when it is lifted by the projecting portion of the

cotton.

The stoppered tubes are then to be packed into a square wire basket which fits into the hot-air sterilizer, and heated in this, with the door closed, until the temperature reaches

about 150° C. The object of this heating is not to sterilize the tubes and cotton stoppers, but to mould the stoppers to the shape of the test-tubes, so that they can readily be replaced when removed in the subsequent filling of the tube with nutritive material. In packing the tubes into the square wire basket as many as possible should be placed with the cotton stopper uppermost, and the remainder of the space in the basket above the tubes may be filled with tubes placed on their sides.

PREPARATION OF CULTURE-MEDIA. Bouillon.- Formula for 1000 c.c.:

500 grams, or about 1 pounds, of lean beef, finely minced, which can be obtained in the shops under the name of Hamburg steak, is thoroughly mixed with 1000 c.c. of ordinary tap-water and allowed to stand over night or for some hours in a cool place. The mixture is then boiled in a saucepan over the gas stove for about half an hour, and next filtered through filter-paper to obtain the clear infusion of the beef free from the coagulated albumin and shreds of tissue. This clear beef-infusion is then turned back into the saucepan, which should be clean, and to it are added 10 grams of pepton (Witte) and 5 grams of sodium chlorid. The mixture is next to be boiled until all these substances are dissolved, stirring frequently with a glass rod, and is then to be neutralized, for it has a decidedly acid reaction from the acid of the meat.

The neutralization is important and requires care. The reaction required is that of a very faint alkalinity, as is shown by the production of a blue color on red litmus-paper, while no change is produced on the blue litmus-paper. In neutralizing, a 10 per cent. solution of caustic soda is added, a few c.c. at a time at first, and later, two or three drops at a