In former years, nobody thought of asking a physician for permission to get married. He was not consulted in the matter at all. The parents would investigate the young man's social standing, his ability to make a living, his habits perhaps, whether he was a drinking man or not, but to ask the physician's expert advice--why, as said, nobody thought of it. And how much sorrow and unhappiness, how many tragedies the doctor could have averted, if he had been asked in time! Fortunately, in the last few years, a great change has taken place in this respect. It is now a very common occurrence for the intelligent layman and laywoman, imbued with a sense of responsibility for the welfare of their presumptive future offspring and actuated, perhaps, also by some fear of infection, to consult a physician as to the advisability of the marriage, leaving it to him to make the decision and they abiding by that decision. As a matter of fact, as often is the case, the pendulum now is in danger of swinging to the other extreme; for, a little knowledge is a dangerous thing, and the tendency of the layman is to exaggerate matters and to take things in an absolute instead of in a relative manner. As a result, many laymen and laywomen nowadays insist upon a thorough examination of their own person and the person of their future partner, when there is nothing the matter with either. Still, this is a minor evil, and it is better to be too careful than not careful enough. I am frequently consulted as to the advisability or nonadvisability of a certain marriage taking place. I, therefore, thought it desirable to discuss in a separate chapter the various factors, physical and mental, personal and ancestral, likely to exert an influence upon the marital partner and on the expected offspring, and to state as briefly as possible and so far as our present state of knowledge permits which factors may be considered eugenic, or favorable to the offspring, and dysgenic, or unfavorable to the offspring. The questions concerning the advisability of marriage which the layman as well as the physician have most often to deal with are questions concerning venereal disease. On account of the importance of the subject, these have been discussed rather in detail under the headings "Gonorrhea and Marriage" and "Syphilis and Marriage." Other factors affecting marriage, either in the eugenic or dysgenic sense, will be discussed more briefly in the present chapter, and more or less in the order of their importance. =Tuberculosis= Tuberculosis, which carries off such a large part of humanity every year, is caused by the well-known bacillus tuberculosis, discovered by Koch. The germ is generally inhaled through the respiratory tract, and most frequently settles in the lungs, giving rise to what is known as pulmonary consumption. However, many other organs and tissues may be affected by tuberculosis.