some large stall or inclosure. They can be fed upon all sorts of vegetables and grasses, and require but little attention.

Methods of Inoculation. I. Inhalation.—Imitating the natural infection, either by loading an atmosphere with the germs in question or by administering them with a spray.

II. Through Skin or Mucous Membrane.

III. With the Food.

Method of Cutaneous Inoculation. The ear of mice is best suited for this procedure. A small abrasion made with the point of a lancet or needle, which has been dipped in the virus. The animal is then separated from the rest and placed in a glass jar, which is partly filled with sawdust and covered with a piece of wire-gauze.

Subcutaneous. The root of the tail of mice is used for this purpose. The hair around the root of the tail is clipped off, and with a pair of scissors a very small pocket is made in the subcutaneous connective tissue, not wounding the animal any more than absolutely necessary, avoiding much blood. The material is placed upon a platinum needle and introduced into the pocket, solid bodies, with a forceps.

To hold the mouse still while the operation is going on a little cone made of metal is used. The mouse just fits in here. There is a slit along the top in which the tail can be fastened, and thus the animal is secure and immobile.

Intravenous Injections. Rabbits are very easily injected through the veins. Mice are too small.

The ear of the rabbit is usually taken. It is first washed with 1-2000 bichloride, which not only disinfects, but also makes the vessels appear more distinct. The base of the ear is compressed to swell the veins. Then a syringe, like the one used for the injection of "tuberculine," a Koch syringe, which can be easily sterilized, is filled with the desired amount of virus and slowly injected into any one of the more prominent veins present. (Fig. 43.)

Intra-peritoneal Injection. This is used with Guinea-pigs mostly. The abdominal wall is pinched up through its entire thickness, and the needle of the syringe thrust directly through, so that it appears on the other side, then the fold let go, the needle withdrawn just far enough so as to be within the cavity.

Inoculation in the Eye. The anterior chamber and the cornea are the two places used. The rabbit is fixed upon a board; the eyelids held apart and head held still by an assistant. A small cut is made in the cornea, a few drops of cocaine having first been introduced in the eye. The material is passed through the opening with a small forceps, and with a few strokes of a spoon it is pushed in the anterior chamber.

For the cornea a few scratches made in the corneal tissue will suffice; the material is then gently rubbed in.

Inoculation of the Cerebral Membranes. The skin and

aponeurosis cut through where the skull is the thinnest. Then the bone carefully trephined, and the dura exposed. In Rabies inoculation, the syringe containing the hydrophobic virus pierces the dura and arachnoid, and the virus is discharged beneath the latter.

Intra-Tracheal. The bacteria can be introduced directly into the trachea, thus coming in contact with the lungs.

Intra-duodenal.-Cholera germs are injected into the intes

tines after they have been exposed, by carefully opening the abdomen. This is done in order to avoid the action of the gastric juice.

Obtaining Material from Infected Animals. The animal should be skinned, or the hairs plucked out, before it is washed, at least the portion where the incision is to be made. Then the entire body is washed in sublimate. Two sets of instruments are required, one for coarser and one for finer work: the one sterilized in the flame; the other, to prevent being damaged, heated in a hot air oven.

The animal, the mouse for example, is stretched upon a board, a nail or pin through each leg, and the head fixed with a pin through the nose. The skin is dissected away from the belly without exposing the intestines. Then the ribs being laid bare, the sternum is lifted up, and the pericardium exposed. A platinum needle dipped into the heart after the pericardium has been slit will give sufficient material for starting a culture. If the other organs are to be examined, further dissection is made. If the intestines were first to be looked at, they would be laid bare first.

In this manner material is obtained, and the results of inoculation noted.

Frequent sterilization of the instruments is desirable.

Koch's Rules in Regard to Bacterial Cause of Disease. Before a microbe can be said to be the cause of a disease, it must

First. Be found in the tissue or secretions of the animal suffering from, or dead with the disease.

Second. It must be cultivated outside of the body on artificial media.

Third. A culture so obtained must produce the disease in question when it is introduced into the body of a healthy animal.

Fourth. The same germ must then again be found in the animal so inoculated.

PART II.

SPECIAL BACTERIOLOGY.

CHAPTER I.

NON-PATHOGENIC BACTERIA.

Special Bacteriology. Under this head the chief characteristics of individual bacteria will be detailed, pathogenic and nonpathogenic being the main divisions. It is usual to describe the non-pathogenic first.

Non-Pathogenic Bacteria. There are 300 varieties of nonpathogenic bacteria, and the list is continually being added to. Bacillus Prodigiosus. (Ehrenberg.) This bacillus, formerly called a micrococcus, is very common, and one of the first noticed, because of the lively red color it forms on vegetables and starchy substances. "The bleeding host," miracles being due to it.

Form.-Short rods, often in filaments, without spores.
Immobile.-Has no automatic movements.

Facultative anaerobic, that is, it can grow without air; but the pigment requires oxygen to show itself.

Growth. Gelatine. Liquefy rapidly.

Colonies. At first white, round points with smooth edge appearing brown under microscope, but soon changing to red. Stab Cultures.-The pigment develops on the surface, the growth occurring all along the line.

Potato is well suited to the growth, the pigment developing after twelve hours. Agar and blood serum growths do well. Temperature.-Grows best at 25° C.

Varieties. By exposure to heat of brood-oven during several generations the power to produce pigment can be temporarily abolished.

(80)

Skyp

The Pigment.-A pigment-forming body is created by the bacillus, and the action of oxygen upon it produces the color. It is insoluble in water, slightly soluble in alcohol and ether; acids fade it, alkalies restore the color. The pigment resembles fuchsin, presenting the same metallic lustre.

Gases. A trimethylamin odor arises from all cultures.
Stain.-Takes all anilin dyes easily in the ordinary way.
Bacillus Indicus. (Koch.) Syn. Micrococcus Indicus.
Origin.-Found in the stomach of an Indian ape.
Form.-Short rods with rounded ends.
matic movements present; facultative anaerobin.
Growth. Gelatine.-Liquefy rapidly.

No spores.

Auto

Colonies.-Round, or oval, granular margins; brilliant red

pigment.

Stab Cultures.-On the surface the pigment shows itself. Grows well on other media.

Temperature.-Grows best at 35° C.

Action on Animals.—In very large quantities, if injected into the blood, a severe and fatal gastro

Plate Colonies.-Round, with transparent centre at first, then
The border is ciliated; little projections

becoming opaque.

evenly arranged.

Potato. A white covering at first, which then changes to a rough brown skin; the skin can be detached in long threads. Temperature.-Spores at ordinary temperatures.

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