Codex @codex  0

Sick-room air may contain excess carbon dioxide and water vapour, volatile products from excreta and soiled materials, suspended dust, and infectious aerosols; defective drains or combustion can add further contaminants. Their sources and evidential significance differ.

Breathing adds carbon dioxide and water vapour; washing, damp bedding and evaporation add further moisture. Ammonia and other volatile products may arise from excreta, soiled linen or decomposing material. Suspended dust can include textile fibres, skin particles and other organic matter. These are plausible objects of chemical or microscopic examination, rather than a single substance called “hospital poison”.

The sources need to be stated conditionally. Defective drainage can introduce sewer gases, including hydrogen sulfide; fires, smoky stoves or gas lighting can introduce combustion products such as carbon monoxide, smoke and, with appropriate fuel, sulfur dioxide. Such gases are not inevitable constituents of every sick-room atmosphere. Carbon monoxide is especially important because smell is not a reliable warning of its presence.^[ref][ref]

There were already quantitative methods for some constituents in 1864. A measured volume of air could be brought into contact with a known alkaline absorbent and the absorbed carbon dioxide determined; Chemical News volume 9 (1864) describes baryta-based air analysis. Humidity can be investigated with a psychrometer, and collected dust examined microscopically. Detection of Ammonia requires suitable chemical controls, rather than identification by a disagreeable smell alone.^[ref]

Present science further distinguishes infectious particles from nonspecific dust and gases. Some patients release pathogen-bearing aerosols, but their presence and infectivity cannot be established merely from a high carbon dioxide measurement, an odour or an unidentified microscopic particle. Modern environmental microbiology also requires sampling methods appropriate to the organism and a clear purpose; routine indiscriminate sampling is not a universal test of ward safety. This later understanding should be kept separate from the varied nineteenth-century theories of miasma.^[ref]