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The classical sequence in lobar pneumonia is congestion, red hepatization, grey hepatization, and resolution. These are overlapping morphological phases, not a clock that every pneumonia follows. An affected lung may contain adjacent areas in different phases; bronchopneumonia has scattered airway-centred foci rather than uniform involvement of a whole lobe. Modern antibiotic treatment often interrupts the textbook sequence.^[ref]

During congestion, the lung is heavy, dark red and boggy but still contains some air. Its cut surface gives a blood-stained watery fluid. Microscopy shows distended alveolar capillaries, oedema within alveoli, and an early cellular exudate, before dense pulmonary consolidation has developed. Reduced alveolar ventilation begins as fluid replaces the normal air space.

In red hepatization, the affected lobe is enlarged, firm, red and substantially airless. Its granular cut surface resembles liver, which explains the name; it is not a transformation into liver tissue. The alveoli are occupied by a mesh of fibrin containing abundant red blood cells and neutrophils, while the alveolar capillaries remain congested. Filling of neighbouring air spaces produces continuous pulmonary consolidation. Associated pleurisy may put a fibrinous exudate on the overlying pleura.

In grey hepatization, pulmonary consolidation remains, but the colour becomes grey, grey-brown or yellowish as intact red blood cells disappear and the fibrin and inflammatory leukocytes dominate. Microscopy shows degenerating neutrophils, debris and persistent intra-alveolar fibrin; the conspicuous vascular engorgement of the preceding phase diminishes. Grey colour by itself does not establish a separate pathogen or mean that an abscess has formed.^[ref]

In resolution, the intra-alveolar exudate is broken down, ingested by macrophages, removed through airways and cleared by absorption. The lobe softens and becomes aerated again. Where the alveolar septa have survived, the architecture can return nearly to normal; an air-space exudate need not become a permanent scar. Failure of clearance may instead lead to organisation and fibrosis; destructive infection can produce abscess or empyema. These are possible outcomes, not obligatory further stages.

A useful examination compares a cut section and a thin histological section from each region, following the alveolar septa to distinguish filling of existing air spaces from destruction of the framework. A dense airless piece may sink in water, but this physical test only shows reduced air content: atelectasis can also sink. The distribution and the microscopy establish why the tissue is airless.

The historical name pityriasis grouped finely scaling eruptions; its varieties were not all one fungal infection. A useful period list is simple or scalp pityriasis, pityriasis rubra, pityriasis versicolor and pityriasis nigra. The names describe distribution or colour, and classifications differed. In particular, “nigra” was sometimes a very dark form of “versicolor,” sometimes a pigmentation disorder with little true scaling. It cannot safely be translated into one present species of fungus.^[ref]

Simple pityriasis, often called pityriasis capitis on the scalp, gives loose, whitish, bran-like scales with little or variable redness. Microscopy of a scale principally shows flattened keratinised epithelial cells and debris. An oily or inflamed scalp can also contain organisms normally living there; this does not make every case identical to pityriasis versicolor. Present descriptions of dandruff and seborrhoeic dermatitis explain many such appearances, but the historical label cannot retrospectively specify the cause of each case.^[ref]

Pityriasis rubra denoted a conspicuously red, scaling eruption, sometimes extensive. Detached scales are again principally epidermal material. A modern skin biopsy may show an inflammatory pattern, but there is no single microscopical organism that defines the historical category. It must not automatically be renamed pityriasis rubra pilaris, a distinct follicular disorder. An extensive red and peeling skin is a pattern requiring causal diagnosis, rather than proof of one infection.^[ref]

Pityriasis versicolor produces irregular pale, yellowish-brown or brown patches, commonly on the upper anatomical trunk, with a fine surface scale. Here the microscopy is especially discriminating: a superficial scraping, cleared with potassium hydroxide, shows clusters of round yeast forms and short curved hyphae within the stratum corneum. Modern classification places the organisms in Malassezia. The older “Microsporon furfur” terminology should not be read as identification of a modern Microsporum dermatophyte. On a histological section the organisms occupy the horny surface layer and are made conspicuous by suitable fungal stains.^[ref]

Pityriasis nigra calls first for verification of what is actually being described. If it is dark pityriasis versicolor, the same superficial yeast and hyphae may be found; if the lesion is pigmentation without a fungal eruption, this finding cannot be assumed. A contemporary discussion explicitly recorded the overlap of nigra and versicolor and disputes over the significance of the supposed parasite.^[ref] Thus epidermal scales are common to the description, but demonstrable fungal structures particularly distinguish pityriasis versicolor. Examine actual scrapings with a optical microscope, compare several fields and use appropriate controls before attributing a different scaling disorder to a fungus.

TODO: Microscopic objects i, ii, iii and iv are unavailable; all four identifications remain undetermined. There are no slide images, observations or preparation details in the supplied paper. This leaf remains incomplete, including each of its four objects.

For each available object separately, begin with low-power microscopy to establish its overall organization, then examine characteristic details at higher power. Record what is visible before assigning a name: the arrangement of biological cells, the proportions and distribution of connective tissue, recognizable boundaries and repeated structures. For a histological section, record its cutting direction and any known histological staining, since orientation and preparation can change its appearance. State the positive features supporting the identification and what further feature would discriminate a close alternative. A drawing should represent the actual field examined, with scale where determinable. None of these observations can be recovered from the labels i–iv alone; the method does not supply the four missing results.