lization of
the disease and the character of the infectious organisms,
particularly with regard to their resistance to the conditions met
with outside of the body. The seat of disease influences the discharge
of organisms; thus, if the disease involve any of the surfaces the
organisms become mingled with the secretions of the surface and are
discharged with these. If the seat of disease be in the lungs, the
throat or the mouth, the sputum forms the medium of extension, which
can take place in many ways. The sputum may become dried, forms part
of the dust and the organisms enter with the inspired air. The
organisms which cause most of the diseases in which the sputum becomes
infectious are quickly destroyed by conditions in the open, such as
the sunlight and drying; street dust does not play so prominent a part
in extension as is generally supposed. Organisms find much more
favorable conditions within houses. It is now generally recognized
that infection with tuberculosis does not take place in the open, but
in houses in which the bacilli on being discharged are not destroyed.
The hands, the clothing and surroundings even with the exercise of the
greatest care may become soiled with the saliva.

It has been shown that in coughing and speaking very fine particles of
spray are formed by the intermingling of air and saliva, which may be
projected a considerable distance and remain floating in the air for
some time. These particles are so fine as to be invisible; they may be
inspired, and their presence in the air forms an area of indeterminate
extent around the infected person within which such infection is
possible. Such spray formation is also an important means of the
extension of infection in the sick individual, for it is continually
formed and inspired. It is in this way that the extreme prevalence of
broncho-pneumonia in infants and young children is to be explained. No
matter what the essential disease, an almost constant finding in young
children after death is small areas of inflammation in the lungs in
and around the terminations of the air tubes. The situation renders it
evident that the organisms which caused the lesions entered the lung
by the air tubes. The mouth of the child is unclean and harbors
numbers of the same sort of organisms as those causing the lung
inflammation; but in the absence of such a mode of infection as is
given by spray formation it is difficult to see how the extension from
the mouth t