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KIDNEYS.

The kidneys are always the seat of hemorrhagic changes, which vary in extent. At times the whole organ is intensely congested, all the glomeruli being visible as minute, deep-red points, while at others it is as a whole not congested, but exhibits in its cortex a number of small, sharply defined, very dark hemorrhagic spots.

From the above-described lesions and symptoms it will be seen that this disease is apparently identical in all particulars with the acute type of hog cholera, and that it is produced without the aid of the hog-cholera bacillus.

The fact that this particular type of hemorrhagic hog cholera is so similar in both symptoms and lesions to the ordinary acute hog cholera supposed to be caused by the hog-cholera bacillus, and that, by our methods of inoculation, without the presence of the hog-cholera bacillus, we have never produced a case of chronic hog cholera, have led us to suspect that possibly in all outbreaks of acute hog cholera there is some other agent besides the hog-cholera bacillus at work, and that in those cases of acute disease where the hog-cholera bacillus is found we have to do, not with a pure infection, but with a mixed infection by hog-cholera bacilli and the organisms which are responsible for the disease which we have just described. In fact, virulent hog-cholera bacilli have been isolated from hogs in which the disease had been produced by inoculation with infective material in which the absence of the bacilli had been proved by filtration, by cultures, and by the inoculation of rabbits or guinea pigs.

If such supposition is well founded, it is quite evident what an important bearing it must have upon the prevention and treatment of hog cholera, and we hope to be able to decide this point positively when the experiments now under way shall have been completed.

Sufficient work has been done to show that this particular form of hog cholera may be prevented by those measures which have been found to be effective in dealing with the ordinary forms of that disease the isolation of sick animals and disinfection of all infected lots with carbolic acid and lime being sufficient to prevent a spread of the disease.

METHODS OF PRODUCING IMMUNITY.

As experiments in this line and also in methods of producing immunity from this disease have been in progress for some years, it seems that, in view of the results, the important points of the investigations should be published, so that the State experiment stations and others, if they so desire, may make experiments on a large scale along the lines of work which have proved most successful.

On account of the often discordant results which were secured some years ago when the Bureau was treating diseased hogs with serum from

animals which in their turn had received large and repeated doses of hog-cholera and swine plague cultures, it appeared that some other factor must be considered in the efforts to produce immunity. The first suggestion of de Schweinitz was that some parasite of the hog, such as the louse, should be studied. This was carefully done, but the results obtained were such as to make it appear that, while a louse might under certain conditions convey disease from a sick to a healthy animal, it was not the important agent in spreading so-called hog cholera.

A large number of specimens of blood from sick and healthy hogs were also examined and, while very small, peculiar, round bodies were found both inside and outside of the corpuscle, and sometimes bodies with distinct ameboid movement were noted, the relation, if any existed, of these bodies to the disease could not be determined satisfactorily. It was noted, however, that in cases of so-called hog cholera the disease could be readily conveyed from a sick animal to a healthy one by giving the latter a subcutaneous injection of the blood serum or defibrinated blood obtained from the former. It was found that a small fraction of a cubic centimeter would produce the disease, though we have in most of our experiments fixed 1 cubic centimeter as the most satisfactory dose for use. As has been indicated above, blood from a diseased animal which was passed through the finest Berkefeld or Chamberland filter produced in hogs the typical disease. This blood had been proved to be free from microorganisms detectable by the ordinary bacteriological methods or by the inoculation of small animals, such as the guinea pig or rabbit, which are known to be very susceptible to the ordinary hog-cholera bacillus. It appeared, therefore, that immunity could be produced by the use of blood in which the disease-producing property had been attenuated or partially neutralized. The experiments have well established the fact, which is also true of the so-called hog cholera, that animals once immunized against this disease will resist repeated large doses of disease-producing blood and also subsequent exposure to diseased hogs in the field.

The basis of the immunity experiments, therefore, has been the usɔ of attenuated and disease-producing liquid or dried blood, or the use of this blood mixed with blood obtained from immune animals, in which animals the immunity has been increased by the injection of large doses of disease-producing blood obtained from hogs known to have the disease; or, in other words, disease-producing blood and antitoxic blood separate and combined have been successfully used.

In order to test the immunity of the treated animals, they were either exposed by inoculating them with known disease-producing blood or by placing them in the field or pen with sick animals.

The previous work of this Bureau has shown very clearly that animals immune from hog cholera are not necessarily immune from swine

plague, or vice versa, and, furthermore, that many different diseases may at times be mistaken for hog cholera. In making practical exposure tests, therefore, it is absolutely necessary to prove the character of the disease by careful autopsies and by the use of a large number of checks, which checks should succumb to the disease in order to prove the positive virulence of the exposure.

Although we are still trying the experiments on a large scale and shall continue them during the coming summer before recommending the details of a plan for practical adoption, we feel that these results of the extensive and laborious experiments which have been carried on by the Bureau for a number of years should be presented now in this concrete form, as it will require a number of months to prepare the detailed reports of the experiments for publication.

The writers have had charge of the general plan of this work and proposed the use of blood from diseased and immunized animals. The practical inoculations and autopsies at the Experiment Station of the Bureau have been carried out under the supervision of Dr. E. C. Schroeder, who also made, at the request of the Chief of the Bureau, some immunity experiments with dried diseased blood. The work in Iowa has been in charge of Dr. W. B. Niles.

INFECTIOUS AND CONTAGIOUS DISEASES OF FARM ANIMALS AND THEIR EFFECT ON AMERICAN AGRICULTURE.a

By D. E. SALMON, D. V. M.,
Chief of the Bureau of Animal Industry.

The subject which I have been asked to discuss at this congress is a very large one and includes so many different elements that it can only be treated in the most general manner in the short time at my disposal. The omission of many important details is therefore a matter of necessity rather than choice. What I shall hope to do is to impress upon you the necessity of controlling the contagious diseases of farm animals and the practical value to the farmers and to the country at large of the efforts of the Federal Government which are being put forth to investigate, to understand, and to control these diseases.

Animal husbandry is one of the most important branches of agriculture, and it has been developed in the United States to a degree which excites the admiration of the world and which justifies every legitimate effort for its assistance and protection. In no other country can you find such an aggregation of farm animals-animals in such amazing numbers, of such value, so highly bred, and so free from discase. Statisticians tell us that we have more than 19,000,000 horses and mules; over 17,000,000 milch cows; 44,500,000 other cattle; nearly 64,000,000 sheep; 47,000,000 hogs, and 250,000,000 fowls of various kinds. The horses and mules are worth $1,200,000,000; the cattle are worth $1,300,000,000; the sheep are worth $168,000,000; the hogs are worth $365,000,000; the fowls are worth about $86,000,000. In round numbers, the total value of these farm animals is $3,119,000,000. This, then, is the tremendous investment of capital which our farmers are holding in domesticated animals. It is generally regarded as simply representing so much wealth, and as a matter of interest to no one but the owners. But we must take a broader view than that of our animal husbandry. The cattle, sheep, hogs, and poultry are a large and essential part of the food supply of the nation, and the horses are necessary for the production of the other part of our food supply. Any cause which reduces the quantity of our food supply or increases the cost of its production makes the conditions of life, especially in the

a Read at the Farmers' National Congress, Niagara Falls, N. Y., September 23 1903.

large cities, more difficult, adds to the distress and misery of that part of the population which at best is merely able to exist, and tends to increase disease and mortality in proportion as its effects are felt. There are also times when through domestic disorder or foreign foes the very life of a nation is at stake, and in such emergencies the food supply has often been an important factor in its preservation. And one of the conditions which undoubtedly adds to the stability of our Government is the abundance and the high quality of our food supply produced by American farmers.

These considerations apply, of course, to all the elements of the food supply as well as to the domesticated animals, but they are of especial interest in connection with animals because of the imported plagues, which are generally preventable, but which often sweep a continent as with fire, depleting the supply of animal food, endangering the public health, and ruining many people who are engaged in agricultural pursuits. A calamity of this kind affects nearly the whole population of a country, depresses business, causes restrictions upon traffic, and often leads to the closing of foreign markets for the animals and animal products of the affected country.

The losses from communicable animal diseases in the United States, considering the large numbers of animals produced, have been moderate as compared with those of other countries, the distance from the Old World having for the most part protected us from the plagues which are most destructive there. Still we have had troubles of our own, and some of them very serious ones, and it is to the consideration of these that most of my time is devoted.

THE CONTAGIOUS PLEURO-PNEUMONIA OF CATTLE.

An imported disease known as the contagious pleuro-pneumonia of cattle led to the establishment of the United States Bureau of Animal Industry and to the active interest which the Federal Government has since shown in the protection of our farm animals from the ravages of communicable diseases. This plague was allowed to slumber in the eastern part of the country for forty years before active measures were inaugurated by the General Government for its suppression. Fortunately the current of traffic was from the West to the East, or the contagion would have been spread beyond the possibility of eradication. Nevertheless, diseased cattle were taken to the West, and the plague appeared in Ohio, Illinois, Missouri, and Kentucky, threatening the entire cattle industry of the country. In this precarious and dangerous situation, when the integrity and the prosperity of the cattle industry for many years in the future, if not for all time, hung in the balance, we had divided counsels. Men who had never seen the disease, for the good reason that they had never looked for it in the places where it prevailed, insisted that it did not exist upon the Ameri

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