THE LUNG PLAGUE. 33 



inflammation of the skin as it is to declare that the lung disease of cattle is an inflamma 

 tion of the air passages and lungs. The local phenomena of the disease are associated with 

 and characterized by inflammatory changes, but the cause in operation inducing all this is 

 peculiar and specific. 



The lung plague is a malignant fever, never generated de novo, so far as reliable obser 

 vation has yet reached, dependent on the introduction of a virus or contagion into the 

 system of a healthy animal. This principle produces a local change if inserted into any part 

 provided with connective or fatty tissue, into which it most readily penetrates. The same 

 local change is produced by its contact with the delicate mucous surface of the bronchial 

 tubes. It adheres, spreads, not unlike cancer, regardless of the nature and importance of the 

 structure it invades, and traverses the lymphatic vessels to form deposits in the neighboring 

 lymphatic glands, but not generally throughout the lymphatic system. At first there is 

 no great intensity of inflammation. Suppuration is only a later complication from the 

 concomitant non-specific change in masses of areolar or connective tissue. Congestion and 

 serous infiltration rapidly surround the spot inoculated. Heat, redness, pain, and swell 

 ing manifest themselves, and the reproduction and extension of the tissue-destroying virus 

 may be judged by the extent of swelling ; the large quantity of yellow gelatinous serosity or 

 exudation which fills the lung tissue thickens the white fibrous structures, blocks up the 

 adipose tissue, in which it displaces the fat corpuscles, and is limited in many cases only 

 by the extent of connective tissue it can invade, by gravitation or otherwise, and the 

 endurance of the animal under a process so prostrating and depletive. 



That all this happens, we have tested by experiment. A susceptible animal is inocu 

 lated in the dewlap, and, at the expiration of a week or nine days, a swelling begins, infil 

 tration extends beneath the chest and abdomen, involves both fore legs, is attended with 

 great fever, prostration, and death. In a second case, a drop of virus is inserted in the tip 

 of the tail. It may produce a scarcely perceptible local change, when suddenly a swelling 

 occurs at the root of the tail. The lymphatic glands there situated enlarge, the areolar tissue 

 is distended with a deposit, such as ordinarily occurs in this disease in the thorax, and so 

 widely does this invade the open tissues of the pelvis as to close the rectum, sometimes 

 to induce retention of urine, and, in the majority of instances, to kill. 



As in the case of variolous inoculation, the effects often vary with the quantity of the 

 virus introduced into a part. Many and deep punctures, especially in soft and vascular 

 textures, will produce malignant variola in inoculating sheep. On the other hand, a single 

 and superficial puncture results in a single pustule and imperceptible general symptoms. It 

 is thus with the lung disease in cattle. 



The slight local change produced by a small quantity of virus, even though it has 

 been impossible to note any systemic disturbance, stands for an attack of the disease, 

 and the animal enjoys almost a perfect immunity from further attacks. 



Viewed in this light, we have to classify bovine pleuropneumonia with the contagious 

 fevers, and we must recognize that it is peculiar and different from all other known diseases 

 of man or beast. The ordinary phenomena of inflammations are but superadded con 

 ditions, and an animal may have the disease without indicating their presence. 

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