CONTAGIOUS DISEASES OP DOMESTICATED ANIMALS. 445 



This form has the granular appearance of that last clescrihed, and on microscopic ex- 

 amination its minute blood-vessels are found distended to their utmost capacity "with 

 accumulated hlood globules. This black consolidation is always sharply limited by 

 the borders of certain lobules or groups of lobules which are connected with a partic- 

 ular air- tube and its accompanjdng blood-vessels, and the artery leading to such 

 lobules is as constantly blocked by a firm clot of blood. The mode of causation is 

 this: the artciy, being in the center of a diseased mass, becomes itself inflamed. As 

 soon as the intiammation reaches its inner coat, the contained blood coagulates; the 

 vein is usually blocked in the same way. The blood formerly supplied by the artery 

 to certain lobules is now an-ested; that in the capillary vessels of these lobules stag- 

 nates ; nutrition of the walls of the capillaries ceases, and these, losing their natural 

 powers of selection, allow the liquid parts to pass freely out of the vessels, leaving 

 the globules only in their interior. More blood continues to enter them slowly from 

 adjacent capillaries supplied from other sources, and as this is filtered in the same way 

 by the walls of the vessels, these soon come to be filled to repletion by the globules 

 only; and hence the intensely dark color assumed. The color is often heightened by 

 the escape of blood from the now friable vessels into the surrounding tissue, and it is 

 by this means that the interlobular tissue is usually stained. (See Plate I.) 



'This black hepatization, or, as it is technically called, infarction, is an almost con- 

 stant occuiTeuce in the disease as seen in New York, and the death and encysting of 

 large portions of lung is therefore the rule. If too extensive, of course, the patient 

 perishes, but not unfrequently a mass of lung measuring four or six inches by twelve 

 is thus separated without killing the animal. 



If at a later stage we open an animal which has passed through the above condi- 

 tion, the following may be met with: A hard resistant mass is felt at some portion of 

 the lung, usually the lower and back portion, and on laying it open it is foimd to con- 

 sist of dead lung-tissue in which the hepatized lobules and interlobular tissues, the 

 air-tubes, and blood-vessels are still clear and distinct, but the whole is separated from 

 the still living lung by a layer of white pus-like liquid, outside which is a dense, 

 fibrous sac or envelope, formed by the development of the surrounding interlobular 

 exi^datiou. From the inner surface of this dense cyst, the firm, thick bronchial tubes 

 and attending vascular systems project in a branching manner like dirty white stalac- 

 tites, and these, with the interlobular tissue thickened by its now firmly organized 

 exudation, may form bands extending from side to side of the cavity. 



At a still more advanced stage the dead and encysted lung-tissue is found to have 

 been entirely softened, and the sac contains but a mass of white liquid debris, or, still 

 later, a caseous mass of its dried, solid matters, ujion which the fibrous covering has 

 steadily contracted, so as to inclose but a mere fraction of its original area. In hun- 

 dreds of post moriems we have only once seen the dead and encysted lung the seat of 

 putrid decomposition, and never found the cavity opening into a previous air-tube. 



There remains to be noticed the condition of the air-tubes and accompanying ves- 

 sels in the diseased lungs. In all cases where we see the starting point of the disease 

 we find in the small tubes leading to the aftected lobules a loss of the natural brill- 

 iancy of the mucous membi-ane, which has become clouded and opaque, and the tissue 

 beneath it infiltrated and thickened. In more advanced cases, and above all in those 

 showing the dropsical condition of the interlobular tissue, we find a similar infiltra- 

 tion into the connective tissue around the air-tubes and their accompanying vessels, 

 and in the hepatized lung this is always seen as a thick, firm, resistant, white material, 

 having the coinpressed and contracted and often plugged air-tubes and vessels in the 

 center. (See Plate I. ) These thickened masses have already been refen-cd to as stand- 

 ing out in stalactite form from the inner wall of the sac in which the dead (necrosed) 

 lung is undergoing solution. 



As to the nature of the phigiie, Dr. Law states that there can be no 

 doubt but it is determiued by an infecting material conveyed in some 

 manner from one beast to another. The intimate nature of this material 

 has never been determiued. No special anatomical element, no specific 

 organism of animal or vegetable origin, has been detected as constant 

 in the diseased organ and iieculiar to it, yet the i)resence of a specific 

 contagium has been fully demonstrated in all the experience of the dis- 

 ease by the author and others. This infecting material, as shown by 

 the records of inoculation, rarely affects the lungs when first lodged on 

 a raw surface of some other part of the body, diifering in this essentially 

 from most other specific disease poisons, which have a definite seat of 

 election in which their morbid processes are invariably established, no 

 matter by what channel they may have been communicated. Since this 



