widely. The herds can be roughly classified as (1) those in an infected district, but themselves free from disease; (2) those known to have been exposed by contact with sick hogs, but which had not developed disease at the time of treatment; and (3) herds in which hog cholera was present and hogs were sick and dying at the time of treatment.

In no case were any of the ordinary methods of combating hog cholera by disinfection and separation of the sick from the apparently healthy practiced. Where disease was present at the time of treatment, the treated animals were allowed to run with the sick along with a number of untreated animals which served as controls, and the success following treatment can therefore be attributed to the action of the serum. In the herds where hog cholera appeared subsequent to treatment, practically all of the treated hogs remained well while more than 65 per cent of the checks died. In the herds which had been exposed but were apparently well at the time of treatment, 4 per cent of the treated animals died while approximately 90 per cent of the checks succumbed. In the herds where disease existed at the time of treatment, and where very great success was not expected, 13 per cent of the treated animals were lost, whereas 75 per cent of the checks died.

These successful field trials, confirming as they do numerous tests carried out under experimental conditions, have convinced us of the efficiency of this method of dealing with hog cholera; and although improvements will undoubtedly be made in many of the details of producing the serum, the method is believed to be now in such condition as to make the practical use of it entirely feasible.

CONFERENCES OF FEDERAL AND STATE REPRESENTATIVES.

In order that the States most concerned in this subject might be brought into closer relation with the work, and also for the purpose of discussing plans for effective coordination of State and Federal work in dealing with hog cholera, twenty-five of the chief hog-raising States were requested to send representatives to Ames, Iowa, where the Bureau of Animal Industry maintains a farm devoted to experiments with hog cholera. In response to this invitation representatives from twenty different States visited Ames and were shown the details of the serum production.

A general discussion at these conferences developed the practically unanimous opinion on the part of State and Federal representatives that the serum should be prepared by each of the States for distribution to the hog raisers, and all State representatives expressed their intention to undertake the work as soon as funds could be secured. At the present time a number of States have actually begun work. If the serum is prepared in sufficient quantities there seems to be no

doubt that a great saving can be effected simply by treating animals in exposed herds or in herds in which the disease has just appeared.

A PLAN FOR CONTROLLING AND ERADICATING HOG CHOLERA BY

SERUM IMMUNIZATION.

If the greatest good is to be accomplished we should not be content simply to reduce the losses from hog cholera, but should undertake systematic efforts to eradicate the disease. The course which hog cholera usually takes when it appears in a neighborhood is well krown. A herd develops the disease, which may not be recognized as hog cholera for several weeks after it has made its appearance. Following this the neighbors' hogs become infected and the disease spreads rapidly, the number of new foci increasing more rapidly as the infected area widens, until finally the losses in a single county may be enormous.

It is evident that in order to control the disease there must be some means of confining it to the original center of infection. This has been attempted by the British Government through the quarantine of farms where hog cholera exists and the slaughter of all infected animals. That such procedures alone do not yield the desired results is shown by the official reports of the continued prevalence of hog cholera in England. In the United States such methods would not be suitable, for, aside from the enormous expense involved, it would, in my opinion, be entirely impracticable to thoroughly disinfect extensive farm premises and to carry out a quarantine which would be effective against such carriers of disease as dogs, crows, buzzards, and other animals.

It has already been stated that the serum from hyperimmunized hogs can be used to protect hogs from hog cholera and that a large saving can be effected if the serum is applied promptly after the disease appears in a herd. Why, then, should not this serum be used as an agent for the eradication of hog cholera? It seems reasonable to believe that it can be used successfully for this purpose, but complete success can not be expected without proper organization and the direction of the work by health authorities.

In order that the possibilities of well-directed work along these lines may be brought to the attention of those who may in the future have this work to perform, the following plan for combating hog cholera through serum immunization is submitted:

1. The serum should be prepared by the State experiment stations or by State live-stock sanitary boards which are properly equipped with laboratory facilities, the efficacy of all serum to be determined by such laboratories before distribution.

2. The field application of the serum should be in the hands of the State live-stock sanitary board or State veterinarian.

3. The State should be organized into districts, each in charge of a deputy State veterinarian or a deputy appointed by the live-stock sanitary board. These districts should be small enough to permit the deputy to exercise close watch over them.

4. The deputy State veterinarian should keep a supply of serum on hand, so that prompt action may be taken when infection appears. 5. Hog raisers generally throughout the State should be informed when the serum is available for distribution, and if necessary compulsory notification of the presence of disease in a herd should be imposed.

6. Upon notification to the State live-stock sanitary board or State veterinarian that hog cholera has appeared in a certain neighborhood, the diseased herd or herds should be immediately quarantined, the premises disinfected as thoroughly as possible, and all hogs on the farm which have been exposed or which are not visibly ill should be treated with serum alone. All hogs on the farm which have not been exposed should be treated by the simultaneous method, and of course the prompt removal of dead animals should be enforced. At the same time all hogs on surrounding farms should be treated by the simultaneous method.

Prompt action of this kind should result in confining the disease to the first herd where disease appeared, though we must admit the possibility of infection being carried beyond the vaccinated belt by birds. If this should occur, the procedure should be the same as in the first case of disease, though the probability of dissemination by birds will not be great, owing to the comparatively small size of the infected area.

With a well-organized live-stock sanitary board and an efficient corps of deputies throughout the State, there seems to be no reason why hog cholera should not be kept well under control and perhaps in time eradicated by proceeding in the way indicated. By starting the work in early spring or summer the task would probably be much simplified and the cost reduced to a minimum.

Aside from the eradication of hog cholera, it seems that an important saving to swine breeders and to the hog industry in general can be accomplished through the protective inoculation of purebred hogs. Some of these hogs represent years of patient effort on the part of breeders, and their loss is a loss to the swine industry in general, which depends for its success in great measure upon the development and preservation of the superior characters possessed by these purebred animals.

There is no doubt that the hog raisers would gladly cooperate with the State authorities and that as a rule any outbreak of disease would be promptly reported, as the farmer would have everything to gain and nothing to lose by so doing.

INFECTIOUS ANEMIA, MYCOTIC LYMPHANGITIS, AND

CHRONIC BACTERIAL DYSENTERY.

By JOHN R. MOHLER, V. M. D.,

Chief of the Pathological Division.

The three diseases known as infectious anemia (swamp fever), mycotic lymphangitis (pseudo-farcy), and chronic bacterial dysentery (Johne's disease) have recently been found to have a greater distribution in the United States than has heretofore been known, and they have therefore assumed importance to sanitary officers, not only on account of their own individual character but also because of the great similarity which they bear to other more common infections for which they may be readily mistaken. A brief discussion of the more important features of each of these three diseases is therefore given below.

INFECTIOUS ANEMIA.

Infectious anemia of horses, known also by a number of other names, as swamp fever, American surra, malarial fever, typhoid fever of horses, the unknown disease, no-name disease, plains paralysis, and pernicious anemia, has recently been the subject of much investigation. The cause of the disease has now been definitely determined as an invisible virus, which is capable of passing through the pores of the finest porcelain filter, like the infection of foot-and-mouth disease, rinderpest, hog cholera, and similar diseases. The disease is most prevalent in low-lying and badly drained sections of the country, although it has been found in altitudes as high as 7,500 feet on marshy pastures during wet seasons. Therefore proper drainage

of infected pastures is indicated as a preventive. It is also more prevalent during wet years than in dry seasons. It usually makes its appearance in June, and increases in frequency until October, although the chronic cases may be seen in the winter, having been. contracted during the warm season.

CAUSE OF THE DISEASE.

It has been conclusively proven that infectious anemia is produced by an invisible, filterable organism, which is transmissible to horses, mules, and asses by subcutaneous inoculation of blood serum. The virus which is present in the blood may be transmitted to a number of equines in a series of inoculations by injecting either the whole

10765-10-15

blood, the defibrinated blood, or the blood serum which has been passed through a fine Pasteur filter, thus eliminating all the visible forms of organismal life, including bacteria, trypanosoma, piroplasma, etc. This virus has also been found to be active in the carcass of an affected animal twenty-four hours after death.

Following the injection of the infectious principle there is a period of incubation which may extend from ten days to six weeks, at the end of which time the onset of the disease is manifested by a rise of temperature. If uncomplicated the infection runs a chronic course, terminating in death in from two months to one and a half years, or even longer. The probability of the virus being spread by an intermediate host such as flies, mosquitoes, internal parasites, etc., is now receiving careful investigation.

From experiments already made it appears that this disease, formerly supposed to be confined to Manitoba and Minnesota, is more or less prevalent in Kansas, Nebraska, Colorado, Wyoming, Montana, North Dakota, and Texas. It also occurs in Europe, having been reported in Germany under the name of infectious anemia and in France as infectious typho-anemia.

SYMPTOMS.

The disease is characterized by a progressive pernicious anemia, remittent fever, polyuria, and gradual emaciation in spite of a voracious appetite. It begins to manifest itself by a dull, listless appearance and by general weakness, the animal tiring very easily. This stage is followed closely by a staggering, swaying, uncertain gait, the hind limbs being mostly affected. (See fig. 23.) There is also noted a weakness and tenderness in the region of the loins, and at the same time the pulse increases in rapidity and may run as high as 70, though weak, stringy, and intermittent. The temperature may rise to 103° F. or higher, remaining high for several days, and then dropping, to rise again at irregular intervals. Toward the end of the disease the temperature occasionally remains persistently high. The horse may improve for a time, but usually this temporary improvement is followed by a more severe attack than the former one. Venous regurgitation is sometimes noticed in the jugular before death. Albumen appears in the urine in the advanced stages of the disease, while the quantity of urine passed is enormous in some cases. Death finally occurs from exhaustion or syncope.

The blood shows a slight decrease in the number of white blood cells, while there is a gradual but marked diminution of red corpuscles, the count running as low as 2,000,000 per cubic millimeter, the normal count being 7,000,000 per cubic millimeter. If the blood is drawn from such an animal, the resulting red clot will be about one-fifth of the amount drawn. Occasionally a slow dripping of