8. The Relation To Tubercle Of Venosity

The Relation To Tubercle Of Venosity (that is, an habitual preponderance of venous blood in the system) and of cyanosis, as resulting from mechanical hindrance at the centres of the organs of circulation and of respiration, is of paramount interest and even of great practical importance. The remarkable exemption from tubercle brought about by these conditions induces us to set forth the relevant facts, as nearly as may be, in their natural order. They determine the venous constitution in various ways, generally conforming in this, that they prevent the arterializing of a sufficiency of blood; whilst they engender cyanosis by hindering the return of blood to the right chambers of the heart, the said blood being arrested in the veins, and consequently in the capillaries generally. The relevant facts, ranged in a twofold series, according as the venous habit and cyanosis are dependent upon the heart or the lungs, are as follows:

(a.) The first place is due to the fact, confirmed by daily experience and convenient as a starting-point for the ensuing considerations; namely, that persons laboring under enlargement (dilatation, hypertrophy, and their complications) of the heart, whether primary or superinduced by mechanical obstruction at its orifices, do not contract tuberculosis.

(b.) Nor does tuberculosis co-exist with such congenital vices of formation in the heart or the great arterial trunks [absence, insufficiency, coarctation of either, persistence of ductus arteriosus, &c] which, with their complications, result in venosity and cyanosis, and, as the anatomical measure of their significance, in augmented volume of the heart.

(c.) Next in the series we have to mention the immunity afforded by many acquired anomalies of arterial trunks, which resemble congenital vices of formation, such as coarctation from compression, obstruction, obliteration, or again by large aneurisms in the vicinity of the heart. Apart from what has already been said on this point, the immunity is due to the mechanical impediment which the overpowering blood-column in the dilated aortal trunk opposes directly to the emptying of the left ventricle, and indirectly to the influx of venous blood into the right heart.

The same immunity is attained in venosity and cyanosis owing to hindrance to the pulmonary circulation; more especially where the impediment reveals its serious character by a dilatation of the right heart.

We may here further adduce:

(d.) The observation that the increased density of the lungs produced by coarctation of the thoracic spaces, in higher grades of lateral curvature of the spine, or in the rickety chicken-breast, excludes tuberculosis. Nay! it is an important fact that, with the establishment of a deformity of the spine in the shape of gibbosity, even when owing to tuberculous caries of the vertebrae, the tubercle-crasis is forever rooted out in consequence of the narrowing of the thoracic spaces.

(e.) The fact that the compression exercised by pleural effusion, and a consecutive, abiding increase of compactness of the one lung, as denoted by a sinking in of the thorax, in like manner extinguishes the tendency to tuberculosis. This effect is the more surely produced, the greater the mechanical obstruction, and the consequent disproportion between the blood-mass and the lung-capillaries pervious to it; and the less competent the other (vicariating) lung is to carry on the function of arterialization.

(f.) The fact that pregnancy arrests the progress of an established tuberculosis; or, as we would correct and extend this proposition, the fact that advanced pregnancy not only arrests a tuberculosis already in being, but also obviates the formation of tuberculosis generally. It is the effect of that embarrassment of the thoracic spaces, and of that resulting condensation of the lung-parenchyma occasioned by upward pressure from the abdomen; in other words, it is based upon a venosity brought about by mechanical means. It is probably for similar reasons that the placenta very rarely, - the foetus perhaps never, becomes tuberculous.

This relation derives further interest from the rapidity with which, after child-birth, that is, after removal of the conditions which prevailed during advanced pregnancy, fibrin-erases with their respective exuda-tory processes, and amongst them the tubercle-crasis and tubercle-deposits, take place, more particularly through the medium of inflammatory stasis.

(g.) To the same class is to be referred the immunity from tubercle arising from every enlargement of the abdominal space, and the consequent narrowing of the thoracic cavity. The exemption allotted to patients afflicted with vast ovarian cystoids probably partakes of this nature.

(h.) Again, the fact that even congenital smallness of the pleural sacs, paired with primitive smallness of the lungs, and, as it mostly is, with an inverse ratio of the development of the abdomen and its viscera, serves as a protection against tuberculosis.

(i.) That in the earliest childhood (with closed foetal passages), owing to a condensed state of the lungs caused by predominant abdomen, tuberculosis occurs, if at all, very rarely.

(k.) The exemption apportioned to those who labor under chronic catarrh, under vesicular emphysema of the lungs, or under bronchial dilatation, was recognized even by Laennec. The empirical recognition of this relation has even led to attempts to cure tuberculosis by the forcible production of those conditions. The real preservative point was, however, overlooked, both here and in another mode of cure aimed at by others, namely, that of closing cavities in the lungs by forcible compression of the thorax. The protective and curative impulse consists, even here, in venosity. And this venosity is a consequence of the destroyed function, the collapse and eventual wasting of numerous pulmonary lobules, through obstruction of their bronchia with mucopurulent secretion; in bronchial dilatation, through the concomitant obliteration of considerable portions of the lung; in emphysema, through lost contractility of the pulmonary texture for expiration, and consequently embarrassed respiration, more especially, however, through the destruction of extensive ranges of the lung-capillaries.

(I.) It will be readily understood that the dropsical crasis, especially when resulting from venosity, excludes tubercle.