The bacillus of malignant edema stains well with ordi

nary cold aqueous solutions of the anilin dyes, but not by Gram's method.

The organism is not a difficult one to secure in pure culture, as has been said, generally contaminating tetanus cultures and being much more easy to secure by itself than its congener. It is most easily obtained from the edematous tissues of guineapigs and rabbits inoculated with garden-earth.

The colonies which develop upon the surface of gelatin kept free of oxygen appear to the naked eye as small shining bodies with liquid grayish-white contents. They gradually increase in circumference, but do not change their appearance. Under the microscope they appear filled with a tangled mass of long filaments which under a high power exhibit individual movement. The edges of the colony have a fringed appearance, much like the hay or potato bacillus.

In gelatin tube-cultures the characteristic growth cannot be observed in a puncture, because of the air which remains in the path of the wire. The best preparation is made by heating the gelatin to expel the air it may contain, inoculating while still liquid, then replacing the air by hydrogen, and sealing the tube. In such a tube the bacilli develop near the bottom. The appearance of the growth is highly typical, as globular circumscribed areas of cloudy liquefaction result (Fig. 101), and may con

In gelatin to which a little

tain a small amount of gas. grape-sugar has been added the gas-production is marked. The gas is partly inflammable, partly CO2. A distinct. odor accompanies the gas-production, and is especially noticeable in agar-agar cultures.

CHAPTER IV.

MEASLES.

IN 1892, Canon and Pielicke, after the investigation of fourteen cases of measles, reported the discovery of a specific bacillus in the blood in that disease.

The organism is quite variable in size, sometimes being quite small and resembling a diplococcus, sometimes larger, and occasionally quite long, so that one bacillus may be as long as the diameter of a red bloodcorpuscle.

The discovery was made by means of a peculiar method of staining, as follows: The blood is spread in a very thin, even layer upon perfectly clean cover-glasses, and fixed by five to ten minutes' immersion in absolute alcohol. These glasses are then placed in a stain consisting of

Concentrated aqueous solution of methylene blue, 40; 0.25 per ct. solution of eosin in 70 per ct. alcohol, 20; Distilled water,

40,

and stood in the incubator at 37° C. for from six to twenty-four hours. The bacilli do not all stain uniformly.

The discoverers of the bacillus claim to have made it grow several times in bouillon, but failed to induce a growth upon other media.

The bacilli do not stain by Gram's method; they seem to have motility; no spores were observed. They were found not only in the blood, but also in the secretions from the nose and eyes. They are said to persist through

out the whole course of the disease, even occasionally being found after the fever subsides.

Czajrowski asserts that the bacillus can be cultivated upon various albuminous media except gelatin and agar. On glycerin agar-agar, especially with the addition of hemotogen, and on blood-serum, they should grow in three or four days with an appearance like that of dewdrops. Under the microscope the colonies are structureless. Mice die of a septicemia after a subcutaneous inoculation.

CHAPTER V.

BUBONIC PLAGUE.

THE bacillus of bubonic plague (Fig. 102) seems to have met an independent discovery at the hands of

Yersin and Kitasato in the summer of 1894, during the activity of the plague then raging at Hong-Kong. There seems to be not the slightest doubt that the micro-organisms described by the two observers are identical.

The bubonic plague is an extremely fatal infectious disease, whose ravages in the hospital in which Yersin made his observations carried off 95 per cent. of the cases. It affects both men and animals, and is characterized by sudden onset, high fever, prostration, delirium, and the occurrence of lymphatic swellings-buboesaffecting chiefly the inguinal glands, though not infrequently the axillary, and sometimes the cervical, glands. Death comes on in severe cases in forty-eight hours. If the case is of longer duration, the prognosis is said to be