The defence of the body can still keep pace with the attack, and even in an advanced stage the infection can be checked in some cases permanently; in others the check is but temporary, the process of softening continues, and large cavities are produced by the destruction of the tissue.

On the inner surface of these cavities there may be a rapid growth of bacilli.
From the lungs the bacilli are carried by the lymphatics to the lymph nodes at the root of the lungs, in which a similar process takes place; this, on the whole, is favorable, because further extension by this route is for a time blocked.

The extension by means of surfaces continues, the abundant sputum which is formed in the lungs and which contains large numbers of bacilli, becomes the vehicle of transportation.

The windpipe and larynx may become infected, the back parts of each are more closely in contact with the sputum and are the parts most generally infected.

A large part of the sputum is swallowed and infection of the intestine takes place, the lesions taking the form of large ulcers.