6 Op. cit.
7 Op. cit., p. 168.
Zeigler has not been able to demonstrate this relation of the tubercle to a blood-vessel—that is, to an artery—but leaves us to infer that they always arise from a capillary vessel, since he maintains that the tubercle is primarily and principally made up of emigrated leucocytes.
Such is a brief résumé of our knowledge as to the histology and mode of formation of tubercle, and such are the opinions—in some particulars agreeing, in others discordant—of those whose investigations and observations the world regards as most complete and accurate. This résumé is doubtless unnecessary and out of place in this article, since this question (the histology and mode of formation of tubercle) has been already discussed in the first volume of this work; but, as in the explanation which is to follow of our views as to what constitutes the tubercular diathesis and what is the mode of formation of tubercle we shall have to frequently refer to the facts above stated, we have thought it best, in order to save repetition and too frequent reference to authorities, to give the above résumé of the present state of the views of pathologists upon the histology of tubercle.
A careful consideration of the foregoing facts ought, it seems to us, to enable us to arrive at a rational and probably correct conclusion as to the mode of formation, as well as the principal etiological factors concerned in the causation, of the miliary tubercle; and we venture to offer the following explanation of the subject as more in consonance with the facts above related than any view which we have seen upon this question:
1. Miliary tubercles always occupy a lymph-space surrounding a capillary blood-vessel. When found, as they quite often are, occupying the wall of a larger vessel, artery or vein, it is still in the lymph-sheath of a capillary of the vasa vasorum that they primarily originated. And it may be said that this is the most dangerous site a tubercle can occupy, because when softening takes place it is so apt to burst into the lumen of the vessel and so produce a general infection.
2. The tubercular process consists at first of an undue or excessive emigration of leucocytes through the walls of a capillary which runs through a lymph-space, and where, of course, the walls of the vessel are less firmly supported. Those cells whose vitality is lowered by the causes which have preceded and excited the process can neither undergo any process of differentiation nor wander on through the lymphatics; they remain in the lymph-space, which they crowd and block up, and finally by their pressure occlude, the capillary vessel from which they emigrated. Until this event occurs they still retain a feeble vitality, and even abortive attempts at proliferation are seen, which, however, only reach the stage of division of the nucleus, the body of the cell meanwhile swelling up by imbibition and thus forming the so-called giant-cell. As soon as the capillary vessel becomes occluded further addition to the incipient tubercle from this source ceases; nutrition is now entirely cut off, and the cells, dying, become a foreign substance, and soon undergo the caseous degeneration. But by their presence they now excite a quasi-inflammatory process in the endothelia lining the lymph-space, and hence we have a secondary addition to the tubercle derived from the proliferating endothelia. Lastly, the inflammatory process extends to the connective-tissue cells around the lymph-space, and embryonic cells (the only cells capable of resulting from connective-tissue inflammation) are added to the mass. This constitutes the proliferating zone, consisting of many nucleated cells and fibro-plastic and spindle-form elements, described by Cornil and Ranvier.8
8 Loc. cit.
As soon as one capillary vessel becomes entirely occluded, the neighboring ones become distended by a collateral hyperæmia, and the same process of cell-exudation or emigration begins; and thus the process goes on until all the capillaries supplied by a single arterial twig take part in the process, and one of the larger tubercles is thus formed by an almost innumerable number of smaller (submiliary) ones. It would seem to be quite probable that the trabeculum which Rindfleisch, Woodward, and Zeigler described, and which Cornil and Ranvier denied, consists of the remains of the connective-tissue fibres which originally existed between the capillaries successively attacked by the tubercular process.
In the lungs this process is usually complicated by a true catarrho-pneumonic inflammation. The tubercle deposited beneath the lining membrane of the air-sacs sets up inflammation in that membrane, giving rise to abundant proliferation of the endothelia as well as emigration of leucocytes, so that the air-sac becomes packed with cells which may finally undergo caseation, and then cannot be distinguished from the original tubercle which started the process. If the eruption of tubercles should be very abundant, life may be destroyed by the pneumonic process before caseation has even begun in the inflammatory products. We have quite recently observed a case of this kind. A man came to the city hospital (Baltimore, Md.) who presented all the rational and physical signs of tuberculosis of the lungs. After about three weeks, during which there was only moderate fever, no notable dulness, and only a few scattered crepitant râles, the temperature suddenly rose to 104° F.; dulness appeared first over the lower third of the right lung, which rapidly extended over that side, and subsequently to the left side, and the man speedily died, comatose and cyanotic. The autopsy showed the most extensive miliary tuberculosis we had ever seen in the human lung; but in addition to the tubercles, which were found in almost every lobule of the right lung, the air-sacs were almost universally filled with a soft, purulent-like matter which oozed from the cut surface, and which could be squeezed out in enormous quantities; myriads of Koch's bacilli were found. It was interesting to note that the apparent starting-point of this tuberculosis was two small cavities in the apex of the left lung surrounded by firmly-indurated walls. Neither of these cavities was larger than the kernel of an ordinary-sized almond, and, as the induration surrounding them did not extend to the surface of the lung, their existence was not recognized before death. The man gave a history of cough and fever, which had lasted several weeks, about three years before his admission to the hospital.