More frequently, however, the reverse of the process above described takes place. That is, a catarrho-pneumonia terminating in caseation and softening sets up tuberculosis through absorption of the caseous pus. Indeed, in the case above related the order of pathological processes was, first, a catarrho-pneumonia of limited extent, a cavity or rather cavities; second, general tuberculosis; and lastly, a secondary catarrho-pneumonia caused by the tubercles. We believe, therefore, that Niemeyer's remark, that "the greatest danger for the majority of consumptives is that they are apt to become tuberculous," is not so absurd as a distinguished American author would have us believe.
The formation, then, of tubercle we believe to be an inflammatory process, in which we have—1st, an exudation of lymphoid cells (leucocytes) into the lymph-spaces, and occlusion by pressure of the capillary vessel from which the cells have escaped; 2d, inflammation and proliferation of the endothelium lining the lymph-space; and 3d, inflammation of the tissues nearest adjacent to the space. If this is simple areolar connective tissue, we have a "proliferating zone consisting of many-nucleated cells and fibro-plastic and spindle-form elements;" if a mucous or serous membrane, the usual products of inflammation of such membrane in other and ordinary cases.
But behind these processes there must exist something else which stands in the relation to them of predisposing and exciting causes. This we believe to be some anatomical and histological peculiarity, congenital or acquired, which gives to the individual that defective organization which is denominated the tubercular diathesis. It seems probable that this diathesis comprises two factors—viz.: 1st, an unusual thinness, and consequently weakness, of the walls of the capillary blood-vessels, which permits and favors a too facile emigration of the leucocytes; and 2d, a diminished or lowered vitality of the leucocytes themselves.
Both of these factors may exist at the birth of the individual as an inheritance from his progenitors, or both may be produced by causes which impair the general nutrition during either intra-uterine life or during the earlier infancy of the subject. Or one of them may exist without the other, and the animal thus escape for a long time, though exposed to the exciting causes of the disease. Sternburg's guinea-pigs (animals peculiarly susceptible to tuberculosis) remained healthy while enjoying the freedom of grassy fields, although inoculated with Koch's bacilli, which were found in their blood and tissues when killed, while those that were confined in cages under bad hygienic conditions speedily succumbed after a similar inoculation.9 If the first of these factors exist, any exhausting disease producing a dyscrasia, habits or hygienic conditions which tend to impair the nutritive functions, even psychological and emotional influences which take away the appetite for food or impair the functions of digestion—anything, in fact, which tends to degrade the quality of the blood and diminish the functional activity of the white blood-cell—may furnish the second factor constituting the tubercular diathesis. Both factors being present, it only requires an uncertain increase of the blood-pressure, causing a dilatation of the capillaries, to ensure that increased leucopedesis which constitutes the first step in the tubercular process.10 A protracted fever, therefore, of any kind, may furnish both the second factor in the tubercular diathesis and the exciting cause of the tubercular process itself; while any fever or any irritant capable of exciting fever or reaction against its presence occurring in man or other animal that happens to have the complete tubercular diathesis may excite tuberculosis. Koch's bacillus will undoubtedly excite tuberculosis in animals (and probably also in man) that have the tubercular diathesis complete; but it does so only by exciting that inflammatory and febrile reaction against its presence in the blood which other and perhaps indifferent irritants may also excite. In rabbits and guinea-pigs confined in cages, and therefore under unnatural and unhygienic conditions, it suffices to excite the disease only to introduce the bacillus into any part of their tissues: that it will not do so in guinea-pigs that are healthy and kept under natural conditions and surroundings Sternburg's experiments, alluded to above, clearly prove. It is true that other animals that are regarded as ordinarily non-tuberculous can also be inoculated with the bacillus with affirmative results, provided the bacillus is introduced into the eye or other serous membranes; but we must not forget that the pain and injury of such an operation will almost inevitably produce that deterioration of the health and impairment of cell-vitality which we maintain constitutes so essential a part of the tubercular diathesis. That the bacillus tuberculosis is always found in tubercle is undoubtedly true; but it is there because tubercle furnishes the most favorable and congenial breeding-place for it. Some special microbe is found in almost every special inflammatory product—vibriones in the pus of abscess, gonococcus in urethral inflammation, micrococcus in diphtheria, etc.—but no one, we believe, now holds that these various microbes are the causes of these diseases, since inoculation with pure cultures have given entirely negative results. While we believe, therefore, that the bacillus of Koch can excite tuberculosis in man or animal having the tubercular diathesis, we also believe that it does so because of its property of exciting that amount of irritation and reaction necessary to initiate the tubercular process—a property, however, possessed by many other irritants; and while it is probable that a few cases may be thus produced in man, a vast majority of the cases arise independently of its presence. And hence we maintain that tuberculosis is not a specific contagious disease in the sense that it is only produced by a special contagion, as small-pox and other similar diseases are.
9 Journal of the American Medical Association, vol. iv. No. 12, p. 314.
10 We hold that leucopedesis is a normal physiological process that is always going on during the period of active growth of the individual, as well as during the process of repair.
Primary acute miliary tuberculosis occurs only in the young or early adult period of life, for the reason, perhaps, that persons of the tubercular diathesis can hardly long escape the exciting causes of the disease, and so are attacked early. Persons possessing what may be called the incomplete or partial diathesis may be attacked by a secondary miliary tuberculosis at any, even the most advanced, age; but it will be found that in all such cases of late tubercularization there has occurred a direct infection of the blood by absorption of caseous detritus from a softening cheesy pneumonia or cavity. "In 28 out of 52 cases collected by Litten, it was associated with pulmonary phthisis, and this accords with general experience" (Roberts11).
11 Practice of Medicine, 5th ed., p. 301.
Acute primary general miliary tuberculosis—that is, in which all or nearly all the vascular tissues are attacked at once—must be one of the rarest diseases. Such cases can only occur when the tubercular diathesis is strongly marked and exciting causes of the most active character have been applied. As a rule, tubercular eruptions occur in successive crops, attacking the more vascular organs, as the lungs, cerebral meninges, spleen, liver, serous and mucous membranes, and bones, first and usually in the order given. Laennec's law, that if tubercle is found in any other organ it will also be found in the lung, is undoubtedly true, with the single exception perhaps of tubercular meningitis. If our explanation of the causes and mode of formation of tubercle is correct, we must a priori expect to find that a tissue so soft and spongy as the lung, and which is so vascular and subject to such great and sudden alterations of pressure and relaxation, would naturally be the site of the first formation of tubercle.
SYMPTOMS AND COURSE.—It is impossible to give a clear or lucid description of acute miliary tuberculosis, since there cannot be said to be any constant or pathognomonic symptoms produced by the disease per se. The symptoms present in any given case depend upon the organs involved, and may be said to consist merely of those furnished by such organs when invaded by inflammation. Fever is present in all cases. The grade or height of this fever will depend upon the number and extent of tubercular formations, and to some extent upon the organs involved. It will generally be highest in tubercle of the serous membranes, and of the lungs next. In general miliary tuberculosis the fever is highest, and can be distinguished with difficulty from enteric fever. If the intestinal mucous membranes are involved, and diarrhoea consequently exist, the differential diagnosis will be almost impossible. The fever, following the law of nearly all inflammatory and symptomatic fevers, is usually remittent, and the remissions and exacerbations correspond to the normal diurnal variations of temperature—lowest in the morning, highest in the evening. The remissions are also usually attended with perspiration, sometimes profuse, at others moderate. The patient early falls into that condition of prostration and general exhaustion which speedily comes on in all fevers of high temperature and protracted duration expressed by the term typhoidal state. Even the pains ordinarily complained of in inflammation of various organs are not felt, or if felt at all are seldom mentioned; which perhaps helps to render the diagnosis more difficult. Almost the only exception to this is when the cerebral meninges are early affected, in which case unusually severe headache may be complained of. Cough may be present, but is not more troublesome than in many cases of enteric fever, and is quite out of proportion to the lesions found in the lungs and pulmonary mucous and serous membranes. The expectoration varies, and is sometimes entirely absent. Generally, it is moderate and consists of frothy serum, occasionally streaked with blood. Hæmoptysis is said to be occasionally present, but must be extremely rare. Respiration is notably frequent early in the disease, and in the absence of pronounced physical signs of pulmonary lesions is perhaps one of the most reliable and pathognomonic signs present. Respirations are often as frequent as 60, seldom less than 30, per minute. The pulse is usually rapid, generally hard at first, but soon becoming soft and weak. The rate varies between 110 to 120 to 160 or more late in the disease.