108 REPORT OF THE BUREAU OF ANIMAL INDUSTRY. 



jority of lung diseases, the specific bacteria can not gain a foothold 

 unless there be some disease already existing which has been pro- 

 duced by exposure or parasites, or both. It is a well-known fact that 

 it is more difficult to produce diseases of a general character like an- 

 thrax by introducing virus through the trachea into healthy lungs 

 than by subcutaneous inoculation, as the air passages are well pro- 

 vided with means for resisting the entrance of foreign particles. 



Schutz, in his investigations of swine plague in Germany, was able 

 to reproduce the disease by exposing pigs to the spray from culture 

 liquids simply because he had a more virulent microbe to deal with. 

 He produced, for example, a general septicaemia in pigs by the sub- 

 cutaneous injection of cultures. Numerous subcutaneous inocula- 

 tions made with cultures at the experiment station of the Bureau 

 have in no case produced septicaemia. We must not expect any 

 microbe to grow in the blood and internal organs of healthy inocu- 

 lated animals when it appears there only in rare instances and in 

 very few numbers in animals spontaneously affected with the specific 

 lung disease, and moreover with the TV hole system greatly debilitated 

 thereby. In his investigations of infectious pneumonia in horses 

 Schutz* reproduced the disease with cultures of the specific microbe 

 by direct injection of culture liquid into the lungs through the walls of 

 the thorax. In. a second experiment made by spraying a large quan- 

 tity of culture liquid through a tracheotomy tube directly into the 

 bronchi the lesions found on killing the animal proved less positive. 



Careful observations of the lungs in pigs which have died of hog 

 cholera, of those which have been killed, apparently in good health, 

 and of those of very young animals which died of exposure or lung 

 worms, lead us to conclude that unless the bacteria of swine plague 

 happen to be of exceptional virulence, some slight lung disease, such 

 as atelectasis or lobular broncho-pneumonia, must furnish the starting 

 point from which the remainder of the lung tissue is attacked. In 

 the preceding- article on hog cholera this has been dwelt upon more 

 at length. There it has been shown that in at least one season of the 

 year, the fall, collapse and lobular pneumonia, lung worms, and bron- 

 chitis are very common in young animals. When an epizootic is very 

 severe, and such seem to be quite rare, the healthy lungs of even 

 adult animals may be attacked. Of this state of affairs the epizootic 

 described furnishes a good illustration. 



SOME OBSERVATIONS ON THE GENERAL CHARACTER OF SWINE 



PLAGUE. 



To understand the character of this disease, its mode of invasion 

 and particular seat, a brief description of the pig's lung is necessary: 



When inflated through the trachea after the sternum is removed, and while it is 

 still in its natural position in the thoracic cavity, it will be observed that the surface 

 resting against the ribs laterally is the most extensive. That surface resting upon 

 the diaphragm comes next, while the ventral aspect is the smallest. 



The right lung is made up of four lobes; the left has only three. (In text-books 

 on anatomy the left lung is considered as being made up of only two.) 



In both there is a large principal lobe resting upon the diaphragm and against the 

 adjacent thoracic wall. This lobe forms the major part of each lung. The remain- 

 der, occupying the anterior (or cephalic) portion of the cavity, is made up of two 

 small lobes, one extending ventrally (or downward in the standing position of the 



* Die Ursache der Srustseuche der Pferde. Archiv fur pathologische Anatomie 

 (1887) CVII, p. 356. Archiv fur wissenschaftliche und praktische Thierheilkunde 

 (1887) XIII, p. 38. 



