red color to the tissue. At times this is further heightened by the rupture of the non-friable vessels and the escape of blood into the surrounding tissue. This rupture of vessels and escape of blood is the usual cause of the reddening or blackening of the interlobular tissue, which is normally pale by reason of its paucity of vessels. When this occurs, the coloration of the lung and interlobular tissue is uniformly of a dark red or black,

This black hepatization is of almost constant occurrence in the lungs of cattle affected with this plague, and is the preliminary stage toward the encysting of a mass of dead lung. If the portion of lung affected in this way is too large, of course the animal dies; but if the portion of infected lung is small enough to be compatible with life, the exudation in the surrounding and still vital tissue is developed into a fibrous wall or envelope, in which the dead lung is encysted. Hence, in nearly all cases we find this black hepatization, or, the still more advanced outcome of this, the encapsulement of a mass of dead lung.

If these encysted masses are seen as soon as they have become inclosed in the sac, they are adherent to it on all sides, and their color is still black. If the examination is made later, the surface layers of the capsuled mass are found to have undergone a granular degeneration and a liquefaction into a white, purulent liquid, which surrounds the mass and separates it from the walls of the sac. Later still, the contained dead mass is still further liquefied and reduced, so that the sac has contracted and diminished while its fluid contents have increased. With the lapse of time, too, the dead encapsuled mass undergoes a granular change, and becomes of a pale, yellowish brown. Yet, even now, the different primal elements of the mass are clearly defined, and it is easy to follow the different bronchia, blood-vessels with now granular clots and interlobular spaces.

This process of gradual liquefaction of the contained mass of lung, and contraction of the cyst upon it, goes on for an indefinite length of time, so that, at different stages, we find all gradations, from a large, encysted mass of twelve inches by six, down to a small sac of an inch across, with a quantity of white, purulent fluid, and a mere pellet of solid material. Later still, this may have been entirely liquefied and absorbed, and there remains only a dense mass of white, fibrous tissue, representing the shrunken and now collapsed wall of the sac.

Finally, we have to notice the condition of the pleura covering the lung. As already stated, I believe this to be affected secondarily, and only as the result of the disease of the lung. Nevertheless, it is always early implicated, and its disease being present in the great majority of cases when opened, and being the first and most striking feature when the ribs are raised, it is not surprising that it has got the primary place in the common name given to the malady-pleuropneumonia. In all cases that are at all advanced, the cavity of the chest contains a quantity of liquid varying from a few pints to as many gallons, sometimes yellowish, clear and transparent, at others slightly turbid or opaque and of a slightly greenish or brownish white tint, while in a few exceptional cases it is of a deeper brown or even reddish, from an admixture with blood. This effusion contains granules and cell-forms, and coagulates more or less when exposed to the air.

On the surface of the diseased lung and to a less extent on the inner surface of the ribs, is a fibrinous deposit, varying from the merest follicle to a mass of an inch in thickness, and, in the worst cases, firmly binding the entire lung to the sides of the chest and the diaphragm. These false membranes are usually of a dull, opaque white, though sometimes tinged with yellow, and, in the deeper layers, even bloodstained, especially over a lung in the state of black hepatization. It is noticeable that the oldest of these false membranes are confined to those portions of the pleura which cover diseased lung tissue, while, if any exists on the surface of the healthy lung, it is usually softer and less fibrous, showing its later deposition.

The tendency of these false membranes is to become organized and developed into white, fibrous tissue, which, in contracting, produces a series of changes in the proper tissue of the lung, all, however, tending to impairment of the breathing. If the resulting fibrous bands merely attach the lungs to the ribs, they limit the movements of the former, render breathing less full and deep, and predispose to certain disorders, notably tuberculosis. A recovery, therefore, which leaves the lung firmly bound to the side of the chest by fibrous bands, is by no means to be considered as an unmodified good.

In other cases, in which the false membrane has become a fibrous covering over a portion or a whole lobe of a lung, a section through both shows that the fibrous material in contracting compresses the lung tissue, preventing the full dilation of the air cells, and rendering the breathing less deep and full. In such cases, the individual lobules, exposed on sections of the part so compressed, are seen to be much smaller than those of adjacent healthy parts, and are less crepitant on pressure than the, healthy lung. Again, in the other portions of the lung devoid of such compression, there may be seen irregular, bladderlike elevations on the surface and in the interlobular spaces, which exhale their aerial contents and collapse when pricked. These result from the attempts to fully distend the lung in hurried breathing and from coughing, for a portion being non-dilatable, the remainder must be subjected to the greater strain. As in the case of the adhesions to the ribs, other morbid conditions will often supervene.

Though not connected with the pleura, it is convenient to mention here the compression of individual pulmonary lobulettes by the organized exudation in the interlobular tissue, which, in becoming fibrous and contracting, often compresses the lung tissue so extremely that it is no longer pervious to air, and on section is only seen as small, brownish patches amidst the white network of fibrous bands.

Thus it will be seen, that, in the great majority of cases, even of those that have escaped the black hepatization, death, and encysting of a portion of lung, recovery is rarely a restoration to the healthy condition, but a class of changes are effected in the texture of the lung which seriously interfere with the freedom of breathing, and often lay the foundation of future troubles. At the same time, it must be acknowledged that if such animals are kept quiet, they will often thrive rapidly, or give a generous yield in the dairy.

NATURE OF THE BOVINE LUng Plague.

'The existence of an infecting material is undoubted, but the intimate nature of this agent is unknown. No specific and characteristic microscopic element, either of the nature of a morbid product of the natural structures, or any vegetable or animal organism introduced from without, has ever been demonstrated as existing in the diseased tissues and peculiar to them. Yet the presence of a specific contagion is demonstrated by the history of the disease in all countries, showing that in all newly-invaded lands it occurs by infection alone; and that inoculation of the virus on a susceptible subject produces an affection which protects the system of that animal against any subsequent attack of the disease.

In the lungs, as already mentioned, the changes take place mainly in the connective tissue and lymphatic plex uses, in the walls of the bronchia, and in the interlobular spaces, and respect, to a large extent, the superficial layer of epithelium as well as the ultimate air cells. From this it might be inferred that this is not necessarily a disease of the lungs, but that the connective tissue and lymphatic system, in other parts of the body, would be equally ready to suffer if the germs could gain access to their substance. This view is further countenanced by the results of inoculation of the virulent lung liquids on other parts of the body. The practice of inoculation on many thousands of animals in all parts of the world has shown, that, while the virus is reproduced in the connective tissue in any part of the body, so that the system becomes insusceptible to any future attack, yet such virulent product is not readily extended to the lungs, to be reproduced there, as if caught in the natural way, as would inevitably be the case if this were a disease of the blood, and the lungs the seat of election of the poison. So seldom, indeed, are the lungs involved after inoculation, that it may be fairly inferred that this only occurs where the products of disease in the tail or other seat of inoculation, have escaped upon the air and been inhaled so as to attack the lungs as in ordinary infection. But as the insertion of the disease in the tail or dewlap produces disease of the tail or dewlap and rarely of the lung, so it may be inferred that, when the disease attacks the lung, as it invariably does under ordinary infection, it is because the virus has reached this by inhalation and been virtually inoculated there. An experiment conducted at the Brown Institution, London, in which the virus was injected into the veins, and failed to produce any local lesion in the lungs or elsewhere, tends to support the same conclusion that the connective tissue and lymphatic apparatus are the true seat of the disease, while the epithelial system, whether on the mucous membranes or the blood-vessels, is insusceptible to its ravages. It may even be questioned whether the elements of the blood itself are not unfavorable to the propagation and increase of the poison, for when thrown directly into the blood it failed to seat itself in the lungs, and when inserted under the skin, and certain, as may be supposed, to enter the blood-vessels directly or through the medium of the lymphatics, it still fails, in the great majority of cases, to induce active disease of the lungs.

As bearing upon this question, it may be stated that, in certain other affections, a specific poison, inserted into the tissues, is evidently local

ized there for a definite length of time, and only affects the system at large, or distant organs, when it has given evidence of active prolification in the seat of inoculation. Thus, malignant pustule shows its first effects as a minute vesicle where the poison was inserted, followed soon after by a crop of other vesicles, in the form of a circle round the first; and if, at this early period, the diseased surface is burned out, the system is saved from the otherwise inevitable general infection, and from the fever which so often proves fatal. Diphtheria, too, is no especial disease of the throat, but will develop on any part of the body, where it is deposited on a raw surface, and is for some time confined to such surface. The same remarks may be made of inoculated syphilis and glanders, which show the lesions first in the seat of inoculation. Even in cases of hydrophobia, with protracted incubation, the seat of the bite usually becomes red, congested and itchy, as probably indicating the prolification of the poison, before the general symptoms of hydrophobia come on.

And the question which I shall not attempt to solve, with my present light, but which is worthy of consideration, is, whether the apparent insusceptibility of the epithelial layers will not explain the occasional protracted period of incubation. The virus, drawn into the smaller bronchial tubes, falls upon the insusceptible epithelium, and, if there exists any break or abrasion of this, it may find its way at once into submucous tissue, when its propagation is insured; but, in the absence of such a breach, may it not lodge harmlessly for a time upon the surface, until it can reach the parts beneath the epithelium by a point from which the cells have been accidentally removed, or by the less accessible channels of the muciparous follicles, or ultimate air cells ?

This much may be safely assumed, that when the virus is inhaled on the air it will fall upon one of two points- the air tubes or the air cells and thus begin its baleful work. This is quite in keeping with the early lesions as I have described them above.

1st. If arrested, as it most commonly will be on the air tubes, and if it attacks the most readily most delicate and susceptible partsthe lung of the smaller branches- it will determine the early thickening of the coats of the bronchia and the cloudy swelling of their surface. As the deeper layers of the peribronchial connective tissue are involved, the exudation and cell growth, giving rise to the extensive, thickening already described, will compress the different vessels and obstruct the flow of liquids through them. The lymphatics, as being incomparably the most delicate and compressible, will be the first to suffer and the obstruction of these will lead to engorgement and dropsy of the parts from which they draw the lymph. The lymphatic vessels and networks are marvelously abundant in the interlobular tissue, and few and small in the lung lobules themselves, hence the obstruction of these vessels, as they lead out from a given section of lung, will lead to a dropsical effusion into the interlobular tissue while the inclosed lobules are comparatively unaffected. This sufficiently explains the excessive liquid exudations into the interlobular tissue as seen in the typical form of the disease. The subsequent congestion, exudation and cell prolifiration in the lobules themselves sufficiently account for the subsequent changes in the lung tissue proper.

2d. If, on the other hand, the infecting material succeeds in reaching the air cells, it will of course make its earliest inroads on their delicate walls. Thus will follow the early congestion, redness and consolidation of the lobules and only later the extensive interlobular exudation, when the disease in the connective tissue around the air tubes shall have compressed the accompanying lymphatic vessels and obstructed the flow of lymph. Thus an invasion by the one form there is at first the excessive effusion into the interlobular tissue; an invasion by the other form there is uniform redness and congestion, but for a time no thickening of the interlobular tissue by effusion.

SPECIAL EXPERIENCES IN ARRESTING THE LUNG PLAGUE.

THE QUESTION OF INOCULATION.

For twenty-nine years inoculation has been practiced as a prophylactic of this plague in all parts of the world to which it has gained access, and in the light of this extended experience we ought now to be able to pronounce definitely on its merits. The main points to be considered are: 1. What inoculation for lung plague is. 2. Does successful inoculation prove vicarious of the plague? 3. If vicarious, in what condition is it applicable? 4. In what circumstances is it to be condemned ?

"INOCULATION: ITS AUTHOR, MODE, ETC.

"In December, 1850, Louis Willems, M. D., of Hassalt, Belgium, son of a large distiller, began his essays on inoculation. To determine the susceptibility of different animals, he inoculated with the exudation. matter from diseased lungs 6 rabbits, 23 pea-fowls, a number of chickens, 4 dogs, 3 sheep, 7 hogs and 2 goats, but in all the wounds healed without any unhealthy action. These animals were accordingly set down as insusceptible. Accidental wounds of human beings were equally harmless. He instituted experiments on several cattle which he inoculated with the liquids from healthy lungs. The result was only slight inflammation followed by healing.

He inoculated three cattle, respectively, with blood, buccal mucus and intestinal tubercle, taken from sick cows. These produced but slight inflammation, followed by prompt recovery.

"He inoculated 108 cattle with the pulmonary exudation of diseased lungs. In a period averaging fifteen days after inoculation a swelling occurred in most of these in the seat of inoculation, and though afterward kept in an infected stable, all these animals resisted the disOf fifty uninoculated animals placed in the same stables, seventeen became diseased.

ease.

"He further re-inoculated ten cattle that had been already successfully inoculated, and all the wounds healed promptly without any