Haemoptysis is one of the most common manifestations in phthisis. It is necessary to distinguish between an early and a late haemorrhage.

(A) Early Haemorrhage

In examining the initial lesion in phthisis, whether in the caseous or fibroid form, it is common to meet with alveoli filled with blood, presenting an appearance very similar to that shown in Fig. 358, which is from a haemorrhagic infarction of the lung.

The blood may be so abundant and occupy so many alveoli, as to give quite the character, on a small scale, of the haemorrhagic infarction.

The blood here comes from the pulmonary capillaries, escaping by diapedesis; it does not arise by insufflation, else it would be more mixed with air and broken up. The homogeneous complete filling of the alveoli implies a regular leakage which gradually expels the air. The blood also is often in alveoli which are little altered otherwise, and it is present in a considerable group of alveoli together.

These facts would indicate a local interference with the circulation as a cause of the haemorrhage. Such an interference is liable to occur from the proximity of the branches of the pulmonary artery to the bronchi. The arteries and bronchi run to a large extent parallel, their sheaths continuous, and the inflammatory changes in and around the bronchi which form such an important part of the initial lesion may well exercise pressure on the arteries. This view is confirmed by the fact that in general tuberculosis of the lung a similar haemorrhage is very often present, sometimes to a very aggravated extent. In this • affection the tuberculosis is usually intimately related to the arteries, so that there will be a direct interference with them.

In any case the "haemorrhage is part of the initial lesion, and it is known that the appearance of blood in the sputum is often a very early sign of phthisis.

As the haemorrhage is associated with the earliest lesions it may occur at a time when no symptoms of disease in the lungs are present, and may be the apparent starting point, although not really so. The occurrence of haemorrhage has been regarded as sometimes the origin of phthisis, a view which has been expressed by the term Phthisin ab hoemoptot. This view is without adequate foundation, and the haemoptysis is probably, in every case, evidence of the existence of the initial lesion. It is not improbable, however, that the occurrence of haemorrhage may accelerate the progress of the disease, as the bacilli may possibly find in the blood a suitable nidus, and so exhibit a more rapid growth.

(B) Late Haemorrhage

The haemorrhage described above may occur at intervals throughout the course of the disease, but in advanced cases a much more considerable and not infrequently fatal haemorrhage is liable to occur. In this case the bleeding arises by Rupture of branches of the pulmonary artery which have been partially exposed in the walls of cavities.

As a general rule the arteries in the walls of cavities are obliterated, more especially in the caseous form, but where obliteration has not completely occurred, the wall of the artery being unsupported and perhaps softened- by inflammatory infiltration is liable to give way. Before the actual rupture the vessel wall usually bulges out, so as to form an Aneurysm (see Fig. 375). In this figure the cavity is a bronchiectatic one, and its wall was comparatively unaltered, the aneurysm having arisen purely from want of support. In the caseous form there is softening of the wall of the artery, and the aneurysm has not such a definite sac as in this case.

In cases of this kind the haemorrhage is often very great, but even in the case of a considerable tear it may be stilled by the blood coagulating in the cavity and forming a kind of cap over the aperture.