Pre-existing or complicating lung diseases may mask or alter the ordinary rusty pneumonic sputa. On the day of crisis, when resolution occurs, the sputa usually become abundant and of a creamy-yellow color. But purulent creamy sputa may occur with a complicating abscess and in some cases of purulent infiltration. During the whole course of the disease there may not be a single characteristic sputum, or it may not be present until the fifth, sixth, or even the twelfth day of the pneumonia. Again, the sputa may continue of a brick-dust hue until the ninth or tenth day. There is frequently an entire absence of expectoration in the pneumonia of acute articular rheumatism and in pneumonia of the apex.
Lastly, the sputa may be more or less pigmented, or when venesection or purgation has been extensively practised expectoration may suddenly cease.
In children expectoration is rarely present, but the brick-dust masses may often be detected in the ejected matter after an attack of vomiting. In senile pneumonia expectoration is never an early symptom, and it is liable during any period of the disease to suddenly cease. Rusty sputa occur in only about 33 per cent. of senile pneumonias. They are at first scanty, gray, and frothy, then yellow or catarrhal (sputa cocta). In severe and fatal cases profuse bloody expectoration may be present at the onset. The reason why the viscid (pathognomonic) sputum of pneumonia is so often absent in senile pneumonia is that the stages pass rapidly into each other, and purulent infiltration takes place very early. The day of crisis is not marked by the same changes in the expectoration that mark the crisis in pneumonia of adult life.
A chocolate-looking serous expectoration usually accompanies the so-called typhoid pneumonia.
When examined under the microscope, the sputum is found to contain swollen epithelia, both spheroidal and columnar, red and white blood-globules, minute spherules of fat, and the other elements which were described as filling the alveoli during the stage of red hepatization. (See [Morbid Anatomy].)
Walshe affirms that pus-cells are not found in the brick-dust expectoration of pneumonia. The mucoid cells will often be stained by the liberated coloring matter of the blood, and pigment-granules may be found mingled with the granular débris of its resolving stage. In about 75 per cent. of the cases there will be found in the sputa, when floated in water, casts of the alveoli and bronchioles.30
30 Diagnost. u. Pathognos. Untersuch., 1845, Remak.
The chemical constituents of the sputa are albumen, mucus, and mucin. Different observers have found the sputa to contain tyrosin and sugar. There are two explanations of the acid reaction of pneumonic sputa.31 Verdeil thought it due to the excess of pneumic acid in the inflamed lung. Bamberger claims that it is due to the deficiency in alkaline phosphates.32
31 Gaz. méd., 1851, p. 777, Robin et Verdeil; Chem. Anat. Phys., vol. ii. p. 460 et seq.
32 Wurtzburg Med. Zeitschr., ii., No. 506.