Tuberculosis being due to a living thing is communicable from one person to another and cannot be gotten except by communication from a previous case. The mode of communication of tuberculosis is by contact and the disease is therefore contagious. This contact need not be direct but may be indirect through a place or thing. A room which has been occupied by a consumptive or a thing which has been used by a consumptive may accumulate enough of the contagion to convey the disease to another person who subsequently occupies such a room or uses such a thing. Nowadays the words contagious and infectious are used synonymously although formerly they had different meanings. The old meaning of infection was conveyance of a disease through a force generated outside of the person giving the disease to the person receiving it. Yellow fever, for instance is an infectious disease according to the old meaning of the word because it is carried from one person to another by a mosquito. The contagion of tuberculosis differs, however, from the contagion of such diseases as small pox, measles and scarlet fever, in that it is very much slower and requires longer and more intimate exposure. You cannot get tuberculosis by a single contact with a person who has the disease; you have to be in intimate relationship with such a person for a considerable time. You can get small pox, measles and scarlet fever by a single momentary contact with persons who have these diseases. The slowness and mildness of the contagion of tuberculosis makes the prevention of the disease very easy when properly understood.