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.