134 REPORT OF THE BUREAU OF ANIMAL INDUSTRY. 



tissue firmly adherent to the convex surface of the same lung. In the cephalic 

 lobe were two or three small collapsed masses. The lungs were sound with this 

 exception. 



SOME GENERAL OBSERVATIONS ON THIS EPIZOOTIC. 



As already stated, in the latter part of September three pigs from 

 one herd and one from another in the vicinity of Baltimore, Md. , were 

 found to contain the lesions as well as the germs of two infectious 

 diseases. One of these pigs communicated both diseases to pigs at 

 the Experiment Station. The swine, plague rose rapidly in severity 

 and then fell equally fast, and almost disappeared within a month 

 after its introduction. The hog cholera, however, continued until 

 the middle of January, 1889, with variable severity. Moreover, not 

 all animals took swine plague, while none of them died of that disease 

 alone. Previous observations have shown that swine plague did not 

 last very long, at least not so long as hog cholera when associated with 

 it. That it may, however, become exceptionally severe is proved by 

 investigations made in Iowa in November, 1888, and reported below. 



Before speaking of the characters of the disease as observed in this 

 outbreak, it must be said that it is by no means safe to make deduc- 

 tions as to the lesions caused by one disease germ or another in the 

 same animal when we have a double disease to deal with. Hence 

 the brief statements made must be considered merely as opinions 

 rather than positive statements. The lung disease is especially puz- 

 zling, in so far as the lesions in different lungs and in different parts 

 of the same lungs are of such different character. I am of the opin- 

 ion that swine plague causes a pneumonia essentially catarrhal in 

 character. In this outbreak, however, much of the pneumonia ap- 

 peared croupous, i. e., red, granular. A certain number of cases 

 died of pulmonary hemorrhages, and I am inclined to think that the 

 hemorrhage and the red hepatization were resultants of hemorrhagic 

 lesions of the lung tissue so common in uncomplicated hog cholera. 

 Usually the dependent lobes appeared to be affected with a chronic 

 broncho-pneumonia, upon which the swine plague was grafted sec- 

 ondarily. It was quite common to find the ventral lobes with the 

 air tubes filled with yellowish- white consistent plugs, or else creamy 

 in character, while other portions were involved in simple pneumonia 

 without implication of the air tubes. Knowing, as we do, that 

 broncho-pneumonia is not uncommon both in young pigs free from 

 any infectious disease and in such as die of hog cholera, it is reason- 

 able to suppose that such lungs are especially vulnerable in the pres- 

 ence of swine plague virus. 



In a considerable number of cases lobules were found, chiefly in the 

 middle and cephalic third of the lungs, apparently necrosed. On mi- 

 croscopic examination such lobules contained a variety of bacteria, 

 chiefly streptococci, ranged along the periphery of the lobule in large 

 masses or colonies, which were brought out very well by the Gram- 

 Weigert stain. It is probable that the lobule became necrosed be- 

 cause of the plugging of its vessels by thrombi, and that these bacte- 

 ria invaded it as putrefactive forms. At the same time we must ad- 

 mit that so far as we know the process may be the very opposite. 



Frequently the disease process is still more complicated by lesions 

 due to lung worms. In some lungs the caudal tip of the large prin- 

 cipal lobe on both sides was converted into a solid, rather hard, gray- 

 ish-yellow mass, evidently due to the irritation of lung worms which 

 settle in this locality. It is probable that swine plague may start in 



