THE SUPPRESSION OF TUBERCULOSIS.
THE CASSEL LECTURE.[1]
Although in this lecture I have planned to discuss mainly the suppression of human tuberculosis, my experiences with bovine tuberculosis cannot be omitted; for not only have I strong reasons for believing that bovine tuberculosis plays an important rôle in the etiology of human tuberculosis, but I am also firmly convinced that by means of the knowledge gained from the study of bovine tuberculosis, we shall be able to prevent to a great extent human tubercular consumption, and favorably influence the course of already existing tubercular diseases.
Both human pulmonary consumption and perlsucht of cattle (which often leads to consumption) are caused by minute vegetable organisms, which it is impossible to differentiate either microscopically or culturally,—the tubercle bacilli of Koch. It is impossible to have either tubercular pulmonary consumption or perlsucht without the presence of these tubercle bacilli; and no matter how susceptible to tuberculosis an individual may be, a tubercular infection cannot take place if these bacilli be absent.
In order for the disease to develop, three factors must always be present: first, the susceptible organism; second, the vegetable parasite; and third, the necessary opportunity to infect. Under the last I understand all the conditions necessary to bring the virus to such a part of the living organism as will enable it to enter either into the circulation or into other body juices.
Every human individual is by nature susceptible to the action of tubercle bacilli which have entered his body juices. This is true not only of human but also of bovine tubercle bacilli. I emphasize this now but shall give my proofs later. But not every tubercular infection of the tissues leads to consumption. Frequently the tubercular infection is followed by such slight disturbances of health that it remains latent throughout an entire lifetime and is only discovered at autopsy.
Whether the entrance of tubercle bacilli into the tissue juices of an individual shall end disastrously or not, depends on a large number of factors. Congenital differences in the degree of susceptibility undoubtedly play a subordinate rôle. A more important factor is the degree of virulence of the inoculated virus, and this may fluctuate within wide limits. Of great importance also is the amount of the virus and whether the inoculation is single, repeated, or almost continuous for a longer time. Of transcendent importance, however, are the age of the individual, his physiological or pathological condition at the time of infection, other previous diseases, mode of feeding, occupation, hygienic conditions of his surroundings, etc. In short, all that we understand by the term acquired susceptibility, or acquired predisposition. Finally, I must mention the location and character of the point of entrance of the virus.
We see at once, therefore, that, in the analysis of a tubercular infection, it is not sufficient to have determined the presence of the three necessary factors, susceptibility, the tubercular virus, and the opportunity for infection. If we wish to understand the manifold variety of the reaction phenomena exhibited by an individual infected with tubercular virus, we must thoroughly study all the conditions above mentioned as well as a great variety of accidental conditions.
Nowadays the term tuberculosis is applied to everything which constitutes a change in the organism excited by the entrance into it of tubercle bacilli. In statistics, galloping consumption is thus classed with tubercular local infection of a joint, gland, abdominal organ, of a little nodule in the skin of the face, etc. Calcified as well as other remains of previous lesions are classed as tubercular. We have every reason to praise as a great scientific advance the discovery that in manifestations so varied in their importance to life and health the etiological factor is the same. One must not, however, make the mistake of classing as one and the same thing tubercular infection and consumption and prognosticate an inevitable and painful end on making the diagnosis of tubercular infection. How little the facts justify such a course is seen in the statistics of bovine tuberculosis and will be seen also when I come to speak of the statistics of human tuberculosis.