disinfection should be practiced at once. Among a large number of substances tried in the laboratory only a few were found to meet the requirements of rapidity of action combined with certainty and cheapness. Carbolic acid seems to be useless, as it is expensive, and a considerable quantity is required to destroy the germs. Thus experiments in the laboratory have shown that to kill the virus in liquids 1 part carbolic acid in 100 parts of water is required, whereas 1 part of mercuric chloride in 75,000 parts of water is sufficient. The best disinfectant is therefore mercuric chloride, also called mercuric bichloride and corrosive sublimate. As it is a violent poison to man and animals, it should be very carefully handled. In order to make a solution which is strong enough to act rapidly and with certainty, 1 part of the substance should be dissolved in 1,000 parts of water. This is best accomplished by adding half an ounce to about four gallons of clear water, preferably rain-water. As a pound of corrosive sublimate retails at about 70 cents, the cost of the disinfectant is very small. This solution, which should be made in wooden or graniteware vessels at least half a day before use, should be applied by means of a broom or brush to the flooring, sides, and covering of pens in which diseased animals have staid. All utensils used about the pens, as well as the troughs and other things containing food, should be carefully washed with the solution and afterwards rinsed thoroughly in pure water. Ten minutes' exposure to the disinfectant solution is sufficient for all purposes. As the corrosive sublimate solution attacks many metals, iron and tin utensils should be disinfected with boiling water instead of the mercuric chloride solution. The bowel discharges should be made innocuous by pouring upon them corrosive sublimate solution or mixing them with powdered chloride of lime. In general it may be stated that whatever has come in contact with diseased animals or their discharges should first be disinfected before healthy animals are brought in contact with them. In using the corrosive sublimate solution we must bear in mind that it is poisonous to animals as well as to man, and that to get the desired effect no large quantities need be applied. The surface need simply be moistened with it in order to be disinfected. A spray apparatus, by means of which a spray is deposited, would be most convenient, but such apparatus is expensive and not readily procurable. It is always desirable to moisten the bodies of dead animals with the disinfectant before removing them. Any virus adhering to the surface of the body is thereby destroyed and the danger of disseminating it avoided.

When the disinfectant is not at hand much can be done with boiling water, which immediately destroys the virus. Scalding the troughs and other articles is perhaps better than the use of the corrosive sublimate, especially if they are immersed in the boiling water or flooded with it. Some good may be done by scalding bowel discharges and the flooring of pens, although by doing so the virus which is not destroyed is carried away by the cooling water, which may later on favor its multiplication. In any case it is best to use for pens the sublimate solution first and then scald them.

As it is quite impossible to disinfect the soil with any degree of certainty, it is very desirable that in a herd in which the disease has appeared the still healthy animals be transferred to fresh ground and kept confined. In this way the dangers arising from an infected soil are averted. For a like reason animals should be kept from streams which have become polluted, as it is impossible to disinfect them.

Hence a dry soil, without standing pools of water, should be chosen as long as any suspicion of the disease exists.

Great care should be bestowed upon the food, especially that of a liquid character, which, when infected, will permit the multiplication of the virus and may infect large numbers. Cleanliness in this respect is perhaps the simplest and most universal rule which can be laid down. This simply means that the food should not come in contact with the bowel discharges of diseased animals; that it should not be allowed to stand for more than a few hours before it is consumed; and that the troughs used for feeding should be scalded at least twice a day when there is a suspicion that the virus may be among the animals.

It may seem too laborious or perhaps superfluous to carry out such directions as these. They may be incompatible with the present methods of hog-raising in many parts of our country. They are, however, the only means at present available by which the spread of the virus may be checked. They prevent the soil from becoming saturated with it, and every exertion made towards disinfection destroys so much, and continued efforts may finally destroy it altogether. Moreover, if the disease does appear while measures of prevention are being carried out, it is not so apt to become very destructive, for the severity of the disease depends, as a rule, upon the quantity of virus taken into the system. If this is allowed to accumulate on all sides, much will find its way into the stomach and intestines and cause the most severe disease.

We do not know whether the virus can live in the soil through the winter, but it seems highly probable. Hence thorough disinfection. practiced will lessen the chances for a reappearance of the disease in the following year.

The investigations in regard to vaccination as a means of prevention have not yet led to any results which can be practically utilized, and therefore are still being carried on. The ordinary methods of attenuation, as practiced by Pasteur in obtaining a vaccinal virus for anthrax and rouget, are inapplicable in this peculiar disease, for the unattenuated virus itself is incapable of conferring immunity. The experiments demonstrating this fact are found on another page. Hence any attenuated virus is still less capable of accomplishing this

end.

The use of certain medicines internally to act as preventives may prove of some value, and it is our purpose to carry out some experiments in this direction as well.

The treatment of this disease, as of the great majority of infection diseases, after it has gained a firm hold upon the animal, is not only useless but dangerous; for the animal can only serve to spread the disease. The ulcerations produced in the large intestines can only heal slowly if they are not too extensive, while medicines are of no avail. Those who insist upon a cure for well-pronounced cases of hog-cholera, in which the bowels have become ulcerated, should look upon the disease of typhoid fever in man, in which ulceration also occurs. Through centuries the best physicians have been treating this disease, yet none has ever ventured to assert that he had a cure for these ulcerations. They take the best care of the patient and allow nature to heal the ulcers. Even then they frequently find their patient snatched away at the very threshold of recovery.

PRELIMINARY INVESTIGATIONS CONCERNING INFECTIOUS PNEUMONIA IN SWINE* (SWINE-PLAGUE).

In prosecuting investigations in the West in order to determine whether the disease which has been described in these reports as hog-cholera existed there also, the lesions characteristic of this disease and the specific bacterium were found in Illinois and Nebraska. At the same time another microbe was found, resembling in its microscopical characters the microbe of rabbit septicemia very closely, and associated with disease of the lungs a chronic pneumonia-in the few cases which were examined. Although the investigations concerning the nature of this microbe, its distribution, and the losses it produces, are scarcely begun, we venture the conclusion that it produces an infectious pneumonia in pigs, and that its effect may perhaps be spent upon organs other than the lungs. This conclusion is based upon the facts recorded in the following pages.

Among the post mortem examinations made in the State of Illinois in July, 1886, the following are worthy of attention:

In Marion County, a few miles from Patoka, a herd was found, July 7, of which about ten had died and an equal number were still alive. Through the kindness of the owner several pigs, which were evidently diseased, were killed by a blow on the head. In No. 1 the superficial inguinals were greatly enlarged; ecchymoses were found in the subcutaneous fatty tissue in large numbers on the omentum and the epicardium. The lymphatic glands were as a rule enlarged and purplish, the spleen augmented in size, the major portion of the lungs hepatized, and the remainder interspersed with hemorrhagic foci. The mucous membrane of the stomach and the large intestine was ecchymosed, that of the latter presenting here and there deep ulcers, especially on the ileo-cæcal valve. Cover-glass preparations from the spleen of this case contained no bacteria of any kind. A tube of gelatine into which a bit of spleen had been dropped remained sterile. No. 2, from the same herd, also killed at the time, was affected with a suppurative pyelitis of the right kidney, causing inflammatory adhesions of the large intestine. The mucous membrane of the latter was dotted with innumerable petechiæ and a few ulcers. Cover-glass preparations from the spleen of this animal were equally negative. A tube of gelatine into which a bit of spleen tissue was dropped began to liquefy very slowly. It contained a bacillus and a large oval coccus.

No. 3, from the same herd, killed, had its lymphatic glands generally enlarged and purplish, the spleen dotted with numerous blood-red elevated points, lungs with large carnified areas. The mucous membrane of the large intestine was merely congested. No bacteria seen in cover-glass preparations of the spleen, and a gelatine culture made as before remained sterile.

Several miles east of Champaign, Ill., the disease was appearing in a herd, the owner of which very kindly permitted us to make what examinations we thought advisable. On July 8 two autopsies were made. In No. 4, dead since last night, the lymphatic glands generally were enlarged and purplish. The subcutaneous fatty tissue stained yellow. The peritoneal and pericardial cavity contained a considerable amount of yellow serum. The only other marked lesion observed was an enormous enlargement of the spleen, which was very dark and pulpy. The mucous membrane of the alimentary canal apparently intact. These lesions did not point to hog-cholera. Cover-glass preparations of the spleen were negative. A piece dropped into a tube of gelatine slowly liquefied the latter. A bacillus was found in it, not pathogenic.

A pig (No. 5) which was observed to be very weak, although able to move about when disturbed, was killed for further information. In the subcutaneous tissue over the abdomen were numerous ecchymoses. The inguinal glands were greatly enlarged, cortex purplish, some lobules deeply congested throughout. The abdominal cavity contained a small quantity of colorless serum; the spleen considerably tumefied and covered with blood-red raised points. The lymphatic glands about the

*We shall call this disease swine-plague, in distinction from hog-cholera, just described. See introductory remarks to Diseases of Swine, p. 603.

stomach, as well as the bronchials, were deeply congested, the cortex infiltrated with blood. The epicardium was dotted over its entire surface with minute extravasations. The mucous membrane in the fundus of the stomach and of the entire length of the large intestine covered with closely-set extravasations. Cover-glass preparations, as well as cultures of the spleen, were entirely negative.

Reports of swine-plague from Geneseo, Henry County, made it advisable to make a few post mortem examinations in this section of the State, in order to make sure of the nature of the disease. The losses were very heavy, involving in many places the greater part of the affected herd. July 11 several autopsies were made in a herd about 3 miles from Geneseo. In this herd the disease had been observed about nine days before. At the time three or four large animals had died during the night and a number of others were ill.

No. 6.-Adult black male, in good condition, no signs of decomposition. In the peritoneal cavity there were ecchymoses beneath the peritoneum of the dorsal wall, near the caudal end of the kidneys, at least an inch in diameter. The spleen was enlarged and congested. Whitish patches showing through the serosa of the large intestine were afterwards found to correspond with ulcerations of the mucous membrane. The lymphatic glands in general with congested cortex. The left lung completely solidified, blackish, and everywhere adherent to chest wall. On forcing the ribs apart the lung tissue broke as a watermelon would; from the broken surface a blackish frothy liquid exuded. A portion of the right lung was in the same condition. A fibrinous deposit on the epicardium indicative of pericarditis. In the alimentary tract the mucous membrane of the fundus of the stomach is darkened with extravasations on the ridges of the folds. In the large intestine the mucous membrane is completely covered with punctiform extravasations, in part converted into pigment. În the cæcum and colon are isolated disk-shaped ulcers about one-half inch in diameter, slightly elevated. The center is dark, surrounded by a broad yellowish margin, giving the whole a button-like appearance. On section a whitish tough tissue is found to make up the ulcer and extend to the peritoneum, where it appears as a whitish patch when viewed from the serous surface. Cover-glass preparations of the spleen negative. Two portions dropped into a tube of gelatine and agar-agar respectively gave rise to cultures which will be described

in detail farther on.

No. 7.-A small shoat, having shown signs of disease for a few days, was killed by a blow on the head. The superficial inguinal glands were enlarged and reddened. Both kidneys dotted on the surface with minute petechiæ. On section a few are found in medullary portion. The spleen is dotted with a few blood-red elevated points. Cover-glass preparations of the spleen negative. Cultures remain sterile. No. 8.-Large black sow; died last night. Adipose abundant. In this animal the spleen was enlarged, the medullary portion of kidneys deeply reddened, lungs normal. The mucosa of the large intestine was entirely covered with minute elongated spots of pigment, representing former extravasations. Cover-glass preparations of spleen also negative. A gelatine tube containing a portion of spleen contained a micrococcus. Bits of the spleen introduced beneath the skin of the dorsum of two mice made them ill for a few days. Both finally recovered.

Besides the cultures mentioned in the autopsy notes at least ten others were made at the time by piercing the spleens with a platinum wire and then piercing with it tubes of gelatine or drawing it over the surface of tubes of agar-agar. None of these showed any signs of growth, thus confirming the supposition, derived from the examination of cover-glass preparations, that the specific microbes are either entirely absent from the spleen or else are present in very small numbers.

The lesions found in all but three cases, in which the ulceration of the large intestine was present, were not sufficiently uniform to warrant the diagnosis of hog-cholera. Viewed by the light of later observations, it seems highly probable that the remainder of the animals were affected with a different malady, due to the presence of the microbe to be described later on. The ecchymosis of the large intestine and the congestion and tumefaction of the lymphatics generally differed from the lesions which we have found in hog-cholera. The absence of bacteria from the tissues is also suspicious. There was moreover a partial cirrhosis of the liver in most of the animals examined which we have never encountered in hog-cholera. We must remember, however, that of these eight cases five were killed, perhaps in the early stages of the disease, before the lesions were well

marked. Leaving these observations for future interpretation, when more cases have been examined we will proceed to a description of the bacteriological investigations.

In a few among a large number of tubes bacteria were present. Nearly all were found harmless when inoculated into animals very susceptible to hog-cholera. In two tubes inoculated with bits of spleen from No, 6 two microbes were found which deserve attention.

One grew in both tubes, which was more carefully examined, because it resembled the bacterium of hog-cholera very closely. In liquid media it is actively motile and simulates the form of a bacillus. When stained, however, each individual is resolved into a pair of ovals or very short rods with rounded extremities. A deeply stained narrow border surrounds a comparatively pale body. There seems to be slightly more stained material at the two extremities than in the bacterium already fully described in the last report. It seems a trifle longer than the latter form, but on attempting to confirm this impression by measurement the dimensions were found practically the same. Sown on gelatine plates the colonies appear within twenty-four hours and grow quite rapidly. The deep colonies are spherical, with smooth outline and homogeneous disc. The surface colonies appear as irregular patches, spreading very quickly, and, as a rule, growing far more vigorously than the deep colonies. In tubes containing nutrient gelatine the isolated colonies in the depth of the needle track may grow to the size of pins' heads. On the surface a flat, thin, pearly layer rapidly extends from the point of inoculation, and in from one to two weeks may have covered the entire surface. The margins are irregularly scalloped and lobed, the entire layer often simulating the frost flowers on windows or lace work (Plate V, Fig. 2). On potato, a thick straw-colored shining layer of nearly smooth surface forms, which grows very vigorously and gradually covers the entire cut surface of the potato with a layer 2mm thick. This growth is brighter in color and more abundant than appears in the potato culture of the bacterium of hogcholera. Cultivated in liquids, such as beef infusion with 1 per cent. peptone, the medium becomes very turbid within twenty-four hours. A thin pellicle appears, which soon becomes a thick membrane. A cream-colored deposit forms and accumulates to a considerable extent, while the liquid remains turbid. It will be remembered that the bacterium of hog-cholera grows very feebly in comparison.

No resistant spore state was found, for tubes exposed to 58° C. for fifteen minutes remained sterile; those exposed ten minutes became turbid. The pale, unstained central portion of the bacterium simulates very strikingly the appearance of an endogenous spore, yet they all succumb to the temperature of 58° C., as described. A peculiar property not common to the hog-cholera bacteria described is the coagulation of the casein of milk. If a tube of this liquid, sterilized by discontinuous boiling, be inoculated, it will be solidified within twenty-four hours. The coagulum, contracting later on, leaves a shallow stratum of watery liquid near the surface. The reaction is acid. Grown on gelatine a rather penetrating odor of decomposing flesh is given off. The bacterium of hog-cholera develops no odor whatever in cultures. This microbe, therefore, resembled the bacterium of hog-colera very closely in its microscopic characters, but differed from it in some of its physiological properties. This illustrates how important cultivation experiments are in the determination of specific differences. That it was not the bacterium of hog-cholera was shown by an utter want of pathogenic properties when inoculated into mice and rabbits. Pigs were inoculated and fed; cultures were introduced per rectum without any effect whatever.

In one of the tubes the motile bacterium just described was mixed. with another microbe, which proved to be a very virulent germ. It was obtained pure as follows: A rabbit inoculated with the mixture from a liquid culture made from the original gelatine tube died in seven days, after showing signs of lameness for several days. The inoculated thigh was enlarged, the skin bluish. The subcutaneous connective tissue was of a leathery consistency. The surface of the muscular tissue on the inner aspect of the thigh was of a uniform yellowish gray; this change extended into the muscular tissue to the depth of 3mm (one-eighth inch); the striated appearance was lost. This change also involved the deeper intermuscular septa of the thigh. On the abdomen the subcutis was infiltrated with a blood-stained