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The historical material was a tuberculous or caseous product, whose formation was associated with constitutional susceptibility, poor nourishment and unhealthy living conditions; its anatomical origin was disputed. The word scrofulous material must not be taken to identify a chemically uniform substance deposited from the blood.

In the period's constitutional account, an inherited scrofulous diathesis, defective nourishment, overcrowding, ill-ventilated accommodation and prolonged debilitating illness were thought to favour its formation. Damp or cold surroundings were also blamed, but are not in themselves a sufficient cause of tuberculosis. A contemporary clinical discussion explicitly linked inadequate diet and crowded, badly ventilated dormitories with scrofulous illness.^[ref] Familial clustering could reflect shared exposure and living conditions as well as host susceptibility; it did not establish inheritance of a ready-made morbid deposit.

The modern explanation separates acquisition of Mycobacterium tuberculosis from progression after infection. Infectious airborne particles can reach the alveoli; close exposure and poor indoor air circulation increase transmission. Impaired immunity, malnutrition and some chronic illnesses increase the risk of progression. Thus some old observations about housing and nutrition concerned real risks, while the old constitutional explanation did not identify the infectious cause.^[ref][ref]

The primary sites considered were the pulmonary interstitium, including supporting connective tissue around small airways and blood vessels, and the lining or contents of the alveoli. A cellular nodule in the supporting tissue is structurally different from degenerated inflammatory material filling air spaces. Contemporary authors disputed formation in exuded fluid versus origin from local tissue elements.^[ref]

Under the microscope, a cellular nodule and its degenerated centre look different. In present terminology a tuberculous granuloma commonly contains epithelioid macrophages, lymphocytes and sometimes multinucleated giant cells, with central caseous necrosis. The caseous portion is granular, largely structureless debris with loss of recognizable viable biological cells; lipid droplets and remnants may be seen. Old descriptions of small granular “tubercle corpuscles” did not establish a uniquely diagnostic cell. Caseation can occur in other processes, and a severely degraded specimen may conceal its origin.^[ref]

A discriminating examination therefore samples both the centre and the advancing margin, preserves the relation to alveoli and interstitium in sections, and examines adjoining lung. Modern acid-fast staining, microbiological culture and molecular tests address the infectious cause; they are later methods, not observations supplied by this 1866 paper. Architecture and causal evidence are more informative than the appearance of the debris alone.

The classical contrast is between ulceration centred on intestinal lymphoid tissue in enteric fever and granulomatous, often circumferential ulceration in intestinal tuberculosis. The historical expression continued fever covered more than one illness. The characteristic bowel lesions meant here point especially to typhoid fever; they should not be attributed indiscriminately to typhus or every prolonged fever.

In typhoid fever, Peyer's patches and solitary lymphoid follicles, particularly in the terminal ileum, enlarge and become infiltrated. Their breakdown and necrosis lead to sloughing and ulceration. The larger ulcers characteristically follow the long axis of the intestine, reflecting the shape of the affected aggregated lymphoid patch on the side opposite the mesentery. Depending on their stage, one may see swollen patches, necrotic sloughs, open ulcers or healing surfaces. Depth varies; erosion into a blood vessel can cause haemorrhage, while full-thickness destruction can cause intestinal perforation and peritonitis.

Microscopically, the important cellular component includes swollen macrophages with ingested organisms and cellular debris; this is not simply a dense collection of neutrophils forming an ordinary abscess. The surrounding mucosal architecture may become severely disturbed. These current cellular descriptions refine the gross lesion recognized before the causative organism was identified.^[ref][ref]

In historical phthisis, bowel disease frequently meant intestinal tuberculosis associated with pulmonary tuberculosis. Lesions commonly involve the terminal ileum and ileocaecal region, although other sites occur. Nodules in mucosal or submucosal lymphoid tissue undergo caseous necrosis, coalesce and break through the mucosa. The ulcerated surface tends to spread transversely and may encircle the bowel. The edges can be irregular and undermined, with additional tuberculous granulomas in the wall, serosal surface or draining lymph nodes. Progressive fibrosis may narrow the lumen and produce a stricture; thickened masses as well as ulcers can occur.^[ref]

A section from a tuberculous ulcer may show central caseous necrosis bordered by epithelioid macrophages, giant cells and lymphocytes. A section from an enteric-fever ulcer instead emphasizes destruction of lymphoid patches with macrophage-rich infiltration. A practical anatomical examination records site, orientation, depth, edges, intervening mucosa, serosal nodules and draining lymph nodes, rather than judging one detached fragment in isolation.

Longitudinal lymphoid-patch ulcers favour the classical enteric-fever pattern; transverse, caseating and often stenosing lesions favour intestinal tuberculosis. These are useful patterns rather than absolute rules. Modern microbiological culture, organism-specific molecular tests and appropriately sampled histology can establish the cause when gross appearances overlap.