cum and upper colon, and as would be expected, we find the secondary lesions distributed in precisely the same manner. If we examine a hog dead of cholera after a short sickness we encounter intestinal lesions in which congestion, hemorrhages and early evidences of degeneration predominate. In hogs that have been sick longer, autopsies often reveal a surprising variety of lesions which collectively encompass effects of the struggle between degenerative and regenerative forces, and which reach their most typical form in the "button ulcer."

In considering thoracic lesions, the same general principles apply. If we inject a pig with filtered hog cholera virus, and kill it about seven days later, the lungs, if affected, will show petechia and ecchymoses, most likely appearing on the cephalic and cardiac lobes, but not always confined to these parts. There may also be congestion of the mucosa of the air passages. Both changes are due to the filterable virus. What result would we expect if a secondary invader, capable of producing inflammatory changes, should find its way into lesions thus prepared? Obviously we would expect to find bronchopneumonia, occurring most regularly in the cephalic and cardiac lobes but not always thus limited. It is significant that this is the exact picture presented when secondary infection with Bact. suisepticum takes place.

The urine of hogs suffering with cholera often contains albumin in excessive amounts, and the chlorids frequently are diminished in quantity, or present only in traces. Contrary to what might be expected, blood and hemoglobin are absent, almost without exception.

CHAPTER VI

DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS

EARLY and correct diagnosis of hog cholera is essential in coping with the disease effectively. Often an entire herd is in jeopardy, and if hog cholera is present prompt preventive measures must be taken to save it. The diagnosis involves no great difficulties when many hogs are sick, but in the early days of an outbreak when peracute or otherwise atypical cases are likely to occur, puzzling situations arise which sometimes cause costly delay. Thus in exceptional cases we are justified in making a provisional diagnosis of hog cholera, and in handling the herd in exactly the same manner as we would were a positive diagnosis possible. Experience has taught that we should not be too conservative in regard to taking such a course when the history suggests the disease and when valuable animals are at stake.

In seeking to determine the presence of hog cholera we depend on four considerations: 1. History of the outbreak.

2. Symptoms.

3. Lesions.

4. Animal Inoculation (rarely applicable). History. Securing the history of an outbreak of suspected hog cholera is simply applying knowledge of the ways in which the virus spreads. Usually we find that a hog has died of an unknown cause and a few days later sickness has appeared among its associates. Careful inquiry should be made regarding recent introduction of hogs into the herd, existence of swine disease in the vicinity, adjacent arteries of traffic and source of feed and water supply. Stockyard hogs and others introduced without clear history of previous health should remain under suspicion. Even though they do not themselves contract the disease they may act as intermediate carriers. There is no evidence that hog cholera virus travels through the air but a road or railroad right-of-way may be contaminated by the drip from infected wagons or cars. If the herd is subsisting on garbage and is not immune the circumstances suggest hog cholera. If kitchen swill is being fed inquiry should be made as to whether the kitchen is supplied with market pork.1

In general the facts brought out by the history of an outbreak simply constitute supplementary

1In one instance that came under our observation an outbreak of hog cholera was traced to meat trimmings that were placed in a poultry house. Two small pigs formed the habit of escaping from the pen and eating freely of these trimmings. Both developed hog cholera simultaneously, and later transmitted it to their associates.

evidence tending either to affirm or deny the presence of hog cholera. Unless there is a definite history of direct exposure the history in itself is not conclusive.

Symptoms. Unless several animals are sick it is seldom possible to make a positive diagnosis based on symptoms alone, but the experienced observer is usually fairly certain of his ground. It is essential to remember that early in an outbreak we do not observe the greatly emaciated hog with arched back, straight tail and drooping ears which has been so frequently described and photographed, and which is the product of long sickness. It should also be kept in mind that many of the symptoms observed in acute hog cholera are present in other diseases, and that all of the symptoms that characterize the disease, do not often appear in one animal. Special consideration must be given to a restricted number of the more characteristic symptoms.

In examining a herd for suspected hog cholera one should first see it unaffected by artificial excitement, taking care to observe a tendency in individuals to chill and crawl beneath the litter. Then the animals may be tempted from the nest with feed, observation being made for any that are reluctant to move, or that stagger or weave in the hind quarters. The animals that come greedily to the trough but leave for the nest in advance of