As an argument against the heredity of tuberculosis, Heller re ports an observation concerning some guinea-pigs at the pathological institute in Kiel.
The pigs are descended from a number of animals which were rendered tuberculous with bovine material 14 years ago. All the descendants, some thousands, have always been healthy and strong with the exception of two short periods, during which several animals died of tuberculosis. Heller believes this infection to have been due to poor hay, without however offering any proof of this fact. Considering the great rarity of spontaneous tuberculosis among guinea-pigs, we may interpret these observations in another way: the latent disease may have been transmitted to the descendants, only to become active at the advent of some exciting factor, such as poor fodder. Such analogies may readily be drawn from families descended from tuberculous ancestors where we find a sudden outbreak of tuberculosis in one or more members.
Two facts favor the probability that hereditary tuberculosis is by no means very rare. First, experiments which show how easily we can artificially infect the offspring (Friedmann); second, the recent observations of Schmorl and Geipel as to the relative frequency of placental tuberculosis.
Although a number of cases of tubereulosis—by no means an insignificant number—are of hereditary origin, nevertheless heredity is not to be regarded as the sole nor even most important cause of the fearful scourge. Nor is there an iron law that the offspring of tuber culous parents or of a tuberculous mother must develop tuberculosis. On the contrary, we see that one or another child is spared, whereas others become its victims. Such selection may be seen also in the transference of the disease among members of the same family. We can therefore formulate two conclusions: (1) tuberculosis may be, but is not necessarily, hereditary; (2) tuberculosis may be inherited but may also he acquired. As regards the mode of hereditary transmission, we have the following possibilities: 1. Germinal Transmission. The seed carries with it the germ of the disease: (a) from the father; (b) from the mother.
2. Placental transmission: (a) with tuberculosis of the placenta; (b) without tuberculosis of the placenta.
:3. Transmission intro partum.
The male as well as the female seed may be the source of heredity. As regards heredity from the male, the experiments of Friedmann have shed much light. He injected a solution containing tubercle bacilli into the vagina; of guinea-pigs immediately after coitus, and killed the pigs within a week. In all the embryos tubercle bacilli were found, intracellular and lying within the embryonal cell layer. The organs
of the mothers were in every case healthy; no tubercle bacilli were found in the vaginal or uterine mucous membrane. As the semen of those suffering from genital tuberculosis is almost always infectious, and as we may find tubercle bacilli in the semen, even in the case of general tuberculosis, where the testicle and epididymis are not involved, the possibility of transmission from the father must be regarded as definitely established. Practically, it is of no importance whether the spermatozoon is diseased or whether it is healthy and merely carries a tubercle bacillus with it. Probably, it must be healthy in order that the development of a fcetus may be brought about. The possibility of germinal transmission from the mother is also presented when we consider that ovarian and genital tuberculosis is by no means rare.
We have already considered the question of transmission of tuber, culosis where there is specific disease of the placenta. But is it per haps possible that bacilli may pass through the placenta without caus ing tuberculous lesions; at. least there are experiments which would tend to prove this.
This is of no practical importance on account of the rarity of tuber culosis of the vagina and of the external genitals.
Heredity of tuberculosis by means of the tubercle bacillus must be definitely distinguished from what is termed the predisposition to tuberculosis. By the latter is understood a condition of the tissues which favors a growth of the tubercle bacillus independent of its por tal of entry. A body so predisposed may be likened to a field pre pared for the growth of some special seed. The resistance which every healthy body offers to pathogenic microorganisms is, in such cases, specifically diminished towards the tubercle bacillus. That certain individuals are more susceptible to tuberculosis than others is a fact that was recognized even at the time when the theory of contagion held sole sway. Koch recognizes the importance of predisposition. Besides taking into consideration a strong family tendency to the disease, he believes that the element of time is important.; that the same person is far more likely to acquire tuberculosis at periods when his power of resistance is diminished. Baumgarten, on the other hand, in consequence of the views stated above, gives little weight to indi vidual predisposition. He believes that man has a superlative predis position to tuberculosis, and that therefore this is not capable of being increased in the case of any individual.