(d) Inoculation of the Anterior Chamber of the Eye.-With a cataract-needle a small incision is made at the junction of the cornea with the sclerotic, the aqueous humor is permitted to escape, and the infecting material is introduced. The wound closes and heals rapidly.

(e) Inoculation of the Cavities of the Body.-The needle of the syringe is introduced into the selected cavity (pleural or peritoneal), and the suspension of bacteria is injected. In intraperitoneal inoculation the needle of the syringe, after thorough cleansing of the abdominal wall, is introduced subcutaneously in a horizontal direction; then the syringe is elevated, and the needle pushed on until the disappearance of resistance indicates that the extremity is free in the abdominal cavity.

(f) Subdural Inoculation.-A trephine-opening is made to one side of the sagittal suture in order to avoid injury to the longitudinal sinus, and, with the aid of a curved needle, the fluid is introduced beneath the dura.

(g) Inoculation by Inhalation.-The bacterial mass is minutely subdivided by means of a spray, which is introduced through a tube into a closed space in which the experimental animals are placed.

(h) Inoculation through the Gastro-intestinal Tract.-The food of the animals is saturated with the bacterial fluid, or this is introduced into the stomach by means of a tube, the jaws of the animal being held apart with the aid of a hollow wooden gag, through which an elastic so-called Nélaton catheter is passed carefully into the stomach.

For special purposes (introduction of bacteria into the liver or into the portal vein or into a loop of intestine) celiotomy becomes necessary. After especially careful sterilization of instruments, hands, and field of operation, the cutaneous incision is made, the muscles are divided layer by layer, and, finally, the peritoneum is divided upon a grooved director. At the conclusion of the inoculation the wound is closed by interrupted peritoneal, muscular, and cutaneous sutures, and it is covered with iodoform-collodion.

All of these various inoculations must naturally be carried out with the most rigorous cleanliness. The skin at the point of inoculation must be shaved and washed with soap, solution of mercuric chlorid, alcohol, and ether. All instruments employed in the inoculation are sterilized by boiling in a one per cent. soda-solution. The disinfection

of the ordinary hypodermic syringe is more difficult, and for this reason quite a number of sterilizable syringes (Fig. 36) have been devised (Roux, Koch, Lewin). The ordinary hypodermic syringe is conveniently and safely disinfected by filling it with, and permitting it to remain for from twelve to twenty-four hours in, a five per cent. solution of carbolic acid, and then removing the carbolic acid by repeated rinsing in sterilized water. In dealing with especially infectious and conspicuously resistant bacteria (anthrax and tetanus), however, the syringe of Roux is employed, and it is boiled for ten minutes in a one per cent. solution of soda. In inoculating the anterior

chamber of the eye the greatest care must be taken to secure disinfection of the conjunctival sac. This is cleansed

Fig. 36.-1, Roux's bacteriologic syringe; 2, Koch's syringe; 3, Meyer's bacteriologic syringe.

with a 13000 solution of mercuric chlorid, which is removed by irrigation with sterilized water. Anesthesia is effected by means of boiled cocain-solution.

The inoculated animals are carefully observed, their temperature is taken at regular intervals, the evacuations and the occurrence of convulsions, etc., are noted, and, in short, all manifestations of disease are looked for. Should an inoculated animal die, the autopsy is to be conducted with every precaution. It is usually made as soon as possible after death, in order to avoid the occurrence of putrefaction. The animal, placed upon its back, is stretched upon a board, with somewhat raised borders. The whole surface of the animal is moistened with a solution of mercuric chlorid, in order to prevent the generation of dust. The

abdominal wall is thoroughly cleansed with the same solution, and then, with instruments sterilized in the flame, it is divided and dissected back on either side sufficiently for the flaps to be fastened to the board with small upholsterytacks. After renewed irrigation a fold of peritoneum is raised, the abdominal cavity opened with a freshly sterilized knife, and the peritoneum thrown back on either side as far as possible. Pieces of all the organs (liver, spleen, kidney, possibly testicle) are removed, and placed in sterilized glass jars for further investigation. From the tissue-fluids of the organs and from the blood cover-slip preparations are made, and at the same time cultures are prepared and poured into plates. As a matter of course, the macroscopic appearance of the organ also is observed, and every pathologic alteration is carefully noted. If necessary, portions of the various organs are hardened and cut with the microtome, in order that the distribution of the bacteria in the tissues can be studied subsequently in stained sections.

In opening the thoracic cavity the xiphoid process is raised with sterilized forceps, and the ribs on the left side, and then those on the right, are divided with scissors, and, finally, the manubrium sterni above is divided. The heart is now exposed, and is opened with a sterilized and cooled knife; and cultures, plates, and streak-preparations are made from the heart's blood. At the conclusion of the autopsy the instruments and the dissecting table are thoroughly disinfected, and the animal cadaver is incinerated.

Special circumstances justify at times the holding of the autopsy at a later period, or subsequent investigation of individual organs. Thus, typhoid-bacilli are more easily cultivated from the spleen of a patient dead of typhoid fever, if that organ has been kept for some time, than if it is examined fresh. Also, in the blood of rabbits destroyed by pneumonia the bacteria can be more readily demonstrated about twelve hours after death than immediately after. Under these circumstances an increase of the bacteria in the cadaver must obviously take place.

However valuable animal experimentation often proves, it is, nevertheless, not capable, in every instance, of securing the desired information. It fails frequently, and especially in connection with those diseases that occur as infections exclusively in man-as for instance, cholera, typhoid fever,

etc.; but even in these cases experiments on animals are not useless, for they demonstrate the toxic activity of the bacteria in question, and they lead, above all, to a knowledge of the anti-bodies formed in the blood-serum. Also, the other of Koch's postulates-that a microbe, to be considered as the cause of a disease, must be present only in association therewith-is not fulfilled in certain diseases. Those infections that are due to the bacteria giving rise to inflammation and suppuration are sometimes caused by the one and sometimes by the other of these germs. The clinical picture of these diseases depends less upon the species of infecting bacteria than upon the site at which the infection is localized. This is true of otitis media, of meningitis, of empyema, etc.; at least, we are as yet not in a position with regard to these diseases to set up different clinical pictures in accordance with the various bacterial findings. A streptococcus-meningitis is clinically not sharply differentiated from a pneumococcus-meningitis or from a meningitis caused by staphylococci, etc. The conception of the specificity of bacteria, which is otherwise fully applicable to the etiology of infectious diseases, must be abandoned with relation to these common excitants of inflammation.

PART II.

INFLAMMATION AND SUPPURATION.

Almost all bacteria exhibit under some circumstances inflammatory and suppurative properties (phlogogenic or pyogenic activity). Inflammation and suppuration may also be induced by chemic substances-as, for instance, ammonia, oil of turpentine, etc.; but, above all, by bacterial metabolic products (ptomains, proteids, etc.) when these are cmployed apart from the bacteria. For practical purposes,

however, this purely chemic mode of origin is of no noteworthy importance, and in almost every suppurative and inflammatory process microorganisms are the responsible agents. The bacteria that are found in the large majority of cases in inflammatory and suppurative areas, and that are known as the common (not specific) causes of inflammation and suppuration, are as follows:

1. The so-called pyogenic cocci (staphylococci, streptococci, pneumococci, etc.).

2. The bacterium coli commune, and the entire group of related bacteria.

3. The far less common pneumonia-bacillus of Friedländer.

4. The bacillus pyocyaneus.

MORPHOLOGY OF THE CAUSATIVE AGENTS OF
INFLAMMATION.

Staphylococcus Pyogenes Aureus (Fig. 37).—This appears in the form of spherical nonmotile cells (micrococci), from 0.7 to 1.2 in diameter, generally arranged like bunches of grapes; hence the designation staphylococci. They stain readily with all basic aniline dyes, and also according to Gram's method. The temperature-minimum