SUES. — External to living tissues the conditions for the growth of the bacillus are extremely unfavorable: after an ex posure to sunlight of from a few minutes to several hours, or to diffused daylight from five to seven days, its growth is retarded, its virulence modified, and it is usually destroyed. Direct sunlight is particularly fatal to this germ, and it is in this that we have the explanation of the partial protection against the whole sale infection of rooms and localities frequented by phthisical patients; while the dust in the room of a tubercular in dividual may contain the germ and be capable of carrying the infection, the bacillus under such conditions remains in an inactive state, does not multiply, and gradually loses its virulence, but only awaits, during its slow destruction, a proper soil upon which to alight, and this not infrequently comes with the susceptible individual who cares for the sick and is constantly breathing a germ carrying atmosphere. Dry sputum may retain for months its infectivity, but, as a rule, this is destroyed by its exposure to sunlight, and the disinfecting process is usually complete before the sputum has become sufficiently dried and pulver ized to be air-borne.
—There is no fact to sub stantiate the theory of direct transmis sion from the male through a germ carrying spermatozoon. There is, how ever, experimental proof in animals that the female ovum may be the carrier, but whether this ever takes place in the hu man being is a question, and from a practical point may be cast aside.
Congenital tuberculosis, in the ma jority of instances, occurs from infection through the blood-current; either the bacilli lodge and grow in the placenta or, having passed this tissue, invade the foetal organs and blood; but, considering the prevalence of the disease, congenital tuberculosis may be regarded as one of the rarities in medicine. Children born
of mothers who at the time of concep tion are far advanced in the tubercular process, seldom show at birth any sign of the disease, and inoculations of the foetal tissues into rabbits give negative results.
The commonly-accepted belief of the laity is that the children of tubercular parents inherit directly from them the disease which, harbored for many years in a latent state, under suitable condi tions becomes manifest. Heredity, in the vast majority of instances, means nothing more than the transmission from parent to offspring of tissue pecul iarities, in accordance with that invari able tendency throughout the vegetable and animal kingdoms for each individual to exactly reproduce itself, not only in its form, size, function, and in its na ture, but in its reaction to environment and in its ability to withstand or to be overcome by the action of various poi sons and disease-producing germs; and this is true, not alone of individuals, but of organ and of cell; and it is this sus ceptibility of cell to invasion by the bacillus of tuberculosis, and not the dis ease itself, which has been inherited, just as children have the blue eyes of their mother or the black hair of their father, or the mental trails and physiognomy of either, which stamp them as a family, brothers and sisters of a common flesh and blood. The old expression that the patient has inherited "weak lungs" cov ers the ground, and with the proper soil which, under the influence of our civil ized life, is kept tilled by the depressing of bad food, poor ventilation, and the like; these, with the wide dis tribution and prevalence of the germ, give at some time all susceptible indi viduals their opportunity to become in fected, and, alas, how many take the chance!