our treatment of these diseases has commensurately acquired greater simplicity and certainty. Although, in the opinion of some, the organs of oxygenation have a greater share in its development, than other organs, yet the stomach is no doubt a prominent agent in the production of phthisis. Whenever this organ, in consequence of debility or any abnormal change, does not properly furnish nutriment to the blood through the digestive process, a reduction of vitality must be the consequence.

Baudelocque, however, shows a very intimate connection,-as cause and effect,-between the results of vitiated air and scrofulous disease. But notwithstanding this, we must from reason as well as from experience, conclude, that the effect of vitiated air upon the respiratory organs and through them on the blood, acting coetaneously with the effect of dyspeptic disease of the stomach upon the blood, is much more sure to produce tuberculosis than when the stomach is in a healthy condition.

The illustrations used by Baudelocque, to show the tendency of impure air to develop tubercles, are forcible and convincing. Speaking of the shepherds of his country, who, for the most part, lead an open-air life, he says, that in them the cause of the disease is their habit of sleeping six or eight hours in confined huts which they transport with them, having only a small door, that they close when they enter, and keep closed during the day. A similar injurious effect is produced by the habit of sleeping with the head under the clothes, and the insalubrity of school rooms in which a number of children are assembled together. These causes frequently repeated, are prolific in the development of any latent germs of phthisis which may be existing in the blood.

Close rooms, Dr. Arnott has pithily remarked, "act like extinguishers to the vital flame; and the extinction literally takes place at the point at which the fuel accumulates for want of being burnt off."

Since the blood is the true source of the tubercular deposit, it is not surprising that all the organs of the body are more or less liable to become the seat of the morbid product. Some tissues present a greater proclivity to the deposition than others; and some, as the fibrous and tegumentary tissues, appear to enjoy almost an immunity from tubercle. At the two ends of the scale,

we may place the mucous membranes and fibrous tissues; the former are the native soil for this tree of death; the latter are rarely, if ever affected. There can be little doubt, that this depends, in a measure, upon certain physical laws, influencing the current in the vascular system, and determining the greater or less facility of transudation in the first instance.

To show that the deposit of tubercle is in the mucous membrane of the lungs, is more difficult than to show its location in the mucous membrane of the fallopian tubes and uterus, because these latter organs, on their internal surface, are lined with mucous membrane, so abundant as to be easily recognised. The more slow and the more free from complication, the tubercular disease of the lungs is, in its nature, so much the more readily may be detected the disease of the mucous membrane, and the tuberculous deposit in it.

Dilatation of the air-cells in emphysema has enabled Dr. Alison to distinctly perceive the tuberculous matter contained in these cells. [Edin. Medi-Chro. Trans. vol. i. p. 427.]

[Dr. Sieveking observes," that we may lay it down as a law, regulating the deposit of tubercle, that it is effected at that point of an organ or of a tissue where the smallest amount of pressure is exerted upon the capillary system. This does not exclude the operation of other laws which determine the attraction to any one organ. It does not offer any reason why in one case we find tubercle in the spleen, in another in the mesenteric or bronchial glands, in a third exclusively in the pulmonary tissues; but it seems to embrace the various circumstances modifying the exact site of the deposit in these different parts of the system. The vis a tergo varies but little in the different parts of the capillary system; but the relation to surrounding tissues differs very much. Thus, while the force with which the blood is driven into the interlobular plexuses of the lungs is identical, the pressure which the respective capillary systems meet with in a case of congestion, which implies a tendency to exudation, is necessarily greater in the bone than in the soft parenchymatous structure. No organ is more frequently the seat of tuberculous deposit than the lung, and in none do we find the capillary ramifications of the vessels with so little covering. They almost lie naked on the surface.

Beyond the basement membrane forming air vesicles, and possibly a delicate epithelial layer, there is nothing between the capillary net-work and the atmosphere. We need not, therefore, wonder that the ultimate vesicle, in which the bronchi terminate, is above all other points, that of tuberculous election. The recepticle is ready, the product being in the blood, a slight increase of pressure will overbalance the natural and healthy equilibrium between the external and the internal fluids, and the discharge takes place.

If this view is correct, nothing but a previous change in the ultimate vesicles, or bronchules could give rise to a deposit of tuberculous matter in the intervesicular tissue, in the parenchyma of the lung itself, as contradistinguished from the respiratory cavities. We can suppose that obliteration of a portion of the breathing apparatus might leave the intervesicular texture less resistent than the air vesicles; and, in that case, we should expect to find an interstitial deposit. Whether this does actually occur, I am not prepared to say. I have not seen any appearances that would justify the assumption of a primary interstitial deposit, but I have seen a distinct deposit of tuberculous matter within the air-vesicles, and I have traced its primary deposit in the semi-liquid form, in the solitary vesicle, to the deposit in numerous adjoining vessels, causing destruction of their breathing power and obliteration of the bronchule terminating in them. The ultimate bronchule is free and patulous, and the tuberculous matter fills the vesicle as a bullet fills its mould.

The law, that the tendency to the deposit in an organ, is inversely as the pressure the vessels sustain, or that it is in the ratio of the laxity of the tissues, is supported by the views which are commonly held with regard to the chemical constitution of tubercle. This law, also assists us in explaining, why certain parts of different organs possess so marked liability to become the seat of tuberculous exudation. This feature constitutes an essential difference between tubercle as a mere effusion of a certain constituent of the blood, and those other new formations in which we cannot but see a tendency to independent development, or organization. The most familiar instances of pathological processes with which it may be compared, are the serous effusions, that

take place into the peritoneal cavity, from obstruction to the vena cava or portal system, inducing congestion and consequent liquid discharge at the most yielding points.

If we adopt this view of the subject, it appears to offer an explanation of the circumstances that the apices of both lungs are the chief seats of tubercle, while it tends to show the importance of encouraging the use of all the physical means at our command to promote a free and active circulation of the entire vascular current, and to obviate and anticipate anything approaching to local congestion in the organs and parts of organs which we know to be most liable, at different periods of life, and under different circumstances, to become affected with the disease in question.

The manner in which the law may be applied to the explanation of the predominant proclivity of the pulmonary apices, is simply this:-The upper portions of both lungs are surrounded by more unyielding parietes than the inferior, they have less room for expansion; consequently, if there is any increase in the vascular current supplying these parts, the difference between the pressure of the parietes and of the atmosphere within the vesicles will increase unduly, and effusion will take place into the latter. In acute tuberculosis, we do not observe this peculiar election, because the process is of a more active character; the strain upon the capillaries of the entire organ is greater than they can bear, and we consequently find the deposit takes place with much uniformity throughout the lung.

In chronic forms in which tuberculous deposit generally occurs, the balance of the forces in different parts of the vascular system, is in a measure preserved, and only the very weak points are assailed. There may be other forces which come into play; there may be elective affinities between different tissues, and morbid products with which we are as yet not even acquainted. The circumstance above alluded to, is one of some importance. In scrofulous deposit in the kidneys where does the tuberculous matter invariably present itself? In the loose texture of the cortical substance. The dense basement membrane and firmer epithelial coat, wards off the encroachment; but the feebler texture of the convoluted tubes is unable to repel the enemy.] Another cause of the more frequent location of tubercles in the superior lobes of

the lungs, has been suggested, which seems somewhat plausible, and is a useful hint to the treatment required in tuberculosis. The increased motion of the lower lobes of the lungs, would cause a more ready expulsion from the vesicles of tuberculous deposits, than would take place in the apices. In the vesicles of the apices, on account of their want of expansion, there would evidently be a tendency to accumulation, while in other parts of the pulmonary tissue the reverse would be true. So that, on this hypothesis, there might be an equal amount of tuberculous matter exuded into the vesicles in all parts of the lungs, and yet, on account of its more ready expulsion from one part of the lung than from another, the development of tubercles, as experience verifies, be most active in the apices.

"Tubercles exist in various forms; in fine points, gray and yellow granulations, miliary tubercles; and gray or yellow tubercular masses, softened and cretaceous. Each of these modifications requires a more particular notice.

"1. Pulmonary Granulations.-Gray Granulations.--Miliary Tubercles.-These various names, have been used by authors to describe round, small, translucent, shining, homogenous bodies, often not larger than a millet seed, but varying from this size to that of a pea, which appear to be the primitive state of tubercles. Usually they are of a grayish, but often of a reddish, or of a brownish color; and in some cases they are nearly colorless. Sometimes they are isolated, sometimes clustered in small bunches, or in aggregate masses. In the latter state they are most often found in the upper portions of the lung. But in an isolated form they are sometimes scattered thickly throughout the whole or greater portion of the pulmonary tissue; not unfrequently they are found situated beneath the pleura, producing an irregularity perceptible This is more often the case in children than in

to the touch.

adults.

"2. Gray Tubercular Infiltration.-Laennec defines this as the same kind of matter which forms the granules above described, deposited in the cellular tissue of the lungs in irregular masses, sometimes one, two, or even three inches in cubic dimensions, without definite boundaries, or limited only by the extent of the lobules. It is hard, homogeneous, translucent, and of a grayish