PNEUMONIA, a term used for inflammation of the lung substance. The disease has long been divided into three varieties ( I) Acute Croupous or Lobar pneumonia; (2) Catarrhal or Bron .cho-pneumonia; (3) Interstitial or Chronic pneumonia.
I. Acute Lobar Pneumonia (Pneumonic Fever) is now classed as an acute infective disease of the lung, characterized by fever and toxaemia, running a definite course and being the direct result of a specific micro-organism or micro-organisms. The micrococcus lanceolatus (pneumococcus, or diplococcus pneu moniae) of Frankel and Weichselbaum is present in a large num ber of cases in the bronchial secretions, the affected lung and the blood. This organism is also present in many other infective pro cesses which may complicate or terminate lobar pneumonia, such as pericarditis, endocarditis, peritonitis and empyema. The bacil lus pneumoniae of Friedlander is also present in a proportion of cases, but is probably not the cause of true lobar pneumonia. Lobar pneumonia is an acute endemic disease of temperate cli mates, though epidemic forms have been described. It has a dis tinct seasonal incidence, being most frequent in the winter and spring. Osler strongly supported the view that it is an infectious disease, quoting the outbreaks reported by W. L. Rodman of Frankfort, Kentucky, where in a prison of 735 inhabitants there were 118 cases in one year ; but direct contagion does not seem to be well proved, and it is undoubted that the pneumococcus is pres ent in the fauces of numbers of healthy persons and seems to require a lowered power of resistance or other favouring condition for the production of an attack.
Lobar Pneumonia begins with an acute inflammatory process in the alveoli. The changes which take place in the lung are chiefly three: (1) Congestion, or engorgement, the air cells still contain air. (2) Red Hepatization, so called from its resemblance to liver tissue. In this stage the congested blood-vessels pour into the air spaces of the affected part an exudation which speedily coagulates, causing the lung to become airless and solid. In this condition the lung substance sinks in water. (3) Grey Hepatization. In this stage the lung still retains its liver-like consistence, but its colour is now grey, not unlike the appearance of grey granite. This is due partly to anaemia from pressure of the solidified exudation on the pulmonary capillaries, partly to local accumulation of enormous numbers of white blood corpuscles. The fibrin of the solid exuda tion is now liquefied by a process of autolysis or peptonization by unorganized ferments and the entangled cells undergo fatty de generation ("resolution"). Absorption of this liquefied material is
carried out by the lymphatics and veins and in most cases the lung soon recovers its normal function apparently uninjured. The absorbed exudate is mainly excreted by the kidneys, excess of nitrogen being found in the urine during this period. When resolu tion does not take place, death may occur from extension of the disease and subsequent toxaemia, heart failure, the formation of abscess or, more rarely, gangrene of the lung or from some compli cation. Usually pneumonia affects one lower lobe but it may ex tend to the whole lung or even to parts of both lungs (double pneumonia). In some cases, and particularly in children, the apex of the lung alone is affected. The prognosis of lobar pneumonia depends to a great extent on the previous history of the patient, especially in respect of alcohol ; a chronic alcoholic patient with apical or double pneumonia rarely recovers. The death rate of acute lobar pneumonia in the chief London hospitals is 20%.
Symptoms.—The attack is usually ushered in by a rigor (or in children a convulsion), and rise of temperature to F or more. Pulse and respiration are quickened but disproportionately so that the normal ratio (3 or 4 :I) is replaced by 2 : i or even i : I. The extraordinary muscles of respiration come into play and rhythmic dilatation of the alae nasi is very characteristic. Pain in the side is felt, especially should any amount of pleurisy be present, as is often the case. Cough is an early symptom. It is at first frequent and hacking, and is accompanied with a little tough colourless expectoration which soon, however, becomes more copious and of a rusty red colour, either tenacious or frothy and liquid. The pa tient during the greater part of the disease lies on the back or on the affected side. The urine is scanty, sometimes albuminous, and its chlorides are diminished. In favourable cases, however severe, there generally occurs after six or eight days a distinct crisis, marked by a rapid fall of the temperature accompanied with per spiration and a copious discharge of lithates in the urine. Although no material change is as yet noticed in the physical signs, the patient breathes more easily, sleep returns, and convalescence advances rapidly in the majority of instances.