CHAPTER VIII.

MOUSE-SEPTICEMIA.

IN 1878, during his investigations upon the infectious traumatic diseases, Koch observed that when a minute amount of putrid blood or of meat-infusion was injected into mice the animals died of a septicemia caused by the multiplication in their blood of a minute bacillus to which he gave the name "Bacillus der Mäusesepticämie" (Fig. 106).

FIG. 106.-Bacillus of mouse-septicemia, from the blood of a mouse; × 1000 (Fränkel and Pfeiffer).

In 1885 the bacillus was again brought into prominence by Löffler and Schütz, who found a very similar,

perhaps identical, organism in the erysipelatous disease which attacks the swine of many parts of Europe.

There seem to be certain slight morphological and developmental differences between these two organisms, but Baumgarten, Günther, Sternberg, and others have regarded them as insufficient for the formation of separate species, and have boldly described the organisms as identical. The described differences are, indeed, so very small that I think it well to follow in the path of the observers mentioned, pointing out in the description such points of difference as may arise.

The bacilli are extremely minute, measuring about 1.0× 0.2 μ (Sternberg). Flügge, Fränkel, and Eisenberg find the Bacillus erysipelas suis somewhat shorter and stouter than that of mouse-septicemia: there seems to be a division of opinion upon this point.

Sporulation has been described by some observers, but nothing definite seems to be known upon this point.

Motility is ascribed by some (Schottelius and Fränkel) to the Bacillus erysipelas suis, and is denied to the bacillus of mouse-septicemia by others. The truth seems to be that the motility of both organisms is a matter of doubt. No flagella have been demonstrated upon the bacillus. It grows quite well both at the room-temperature and at the temperature of incubation. It can grow well with or without oxygen, but perhaps flourishes

of the bacillus of mouse-septicemia; × 8c (Flügge).

a little better without than with it.

The colonies upon gelatin plates can first be seen on the second or third day, then appearing as transparent grayish

FIG. 107. Colony specks with irregular borders, from which many branched processes extend (Fig. 107). Fränkel describes them as resembling in shape the familiar branched cells occupying the lacunæ of bone. When further developed the colonies flow together and give the plate a cloudy gray appearance. The gelatin is not

liquefied.

In gelatin puncture-cultures the growth is quite characteristic, and the tendency of the bacillus to grow anërobically is well shown (Fig. 108). The develop

ment takes place all along the line of puncture, but is more marked below than at the surface. The growth takes place in a peculiar form, resembling superimposed disks, each disk separate from its neighbors and consisting of an area of clouded grayish gelatin reaching almost to the walls of the tube. This growth develops slowly, and causes a softening rather than an actual liquefaction of the gelatin.

Upon agar-agar and blood-serum a very delicate, transparent grayish line develops along the path of the needle. The bacillus grows at the room-temperature, but much better at the temperature of the incubator.

The disease affects quite a variety of animals, notably hogs, rabbits, mice, pigeons, and sparrows. The guineapig, which is generally the victim of laboratory experiments, is not susceptible to it.

When mice are inoculated with a pure culture of this bacillus, they soon become ill, lose their appetite, mope in a corner, and are not readily disturbed. As the dis

ease becomes worse they assume a sitting posture with the back much bent; the eyelids are glued together by adhesive pus; and when death comes to their relief, in the course of forty to sixty hours after inoculation, they remain sitting in the same characteristic position.

When the ears of rabbits are inoculated with the bacillus from cases of erysipelas suis, a violent inflammatory edema and distinct redness occurs, much resembling erysipelas. This lesion gradually spreads, involves the head, then the body of the animal, and ultimately causes death.

When swine are affected, they are dull and weak, and have a kind of paralytic weakness of the hind quarters. The temperature is elevated; red patches appear upon the skin and swell and become tender. Death follows in two or three days.

In all animals the anatomical changes are much alike. The disease proves to be a septicemia, and the bacilli can be found in all the organs, especially the lungs and spleen. They are few in number in the streaming blood.

As the organisms stain well by Gram's method, this stain is of great value for their discovery in the tissues, and can be highly recommended.

Most of the bacilli occupy the capillary blood-vessels; many of them are enclosed in leucocytes. The organs in such cases do not appear distinctly abnormal, except the spleen, which is considerably enlarged. The mesenteric and other lymphatics are also enlarged, and the gastric and intestinal mucous membranes are usually inflamed and mottled. The bacilli also occupy the intestinal contents, and Kitt, who discovered them in this position, points out that the infection of swine probably takes place by the entrance, along with the food, of the fecal matter of diseased animals into the alimentary apparatus of others.

Pasteur, Chamberland, Roux, and others have worked upon a protective vaccination based upon the attenuation of the virulence of the organism by passing it through

rabbits. Two vaccinations are said to be necessary to produce immunity. The vaccinated animals, however, may be a source of infection to others, and should always be isolated. Klemperer in 1892 found that the bloodserum of immunized rabbits would save infected mice into which it was injected.

Lorenz in 1894 found an antitoxic substance in the blood of rabbits immunized to the disease. The effect of its injection into other animals is, however, only a temporary immunity.