Practical implications of much of this work have not advanced very far beyond 1887

Direct quote(s) from Carnelley et al. (75)Translation and/or comment (if applicable)
“In order to draw conclusions from an examination of air inside buildings, it is of course necessary to know the state of the outside air.”Always sample both indoor and outdoor air. Most, but not all, studies reviewed in the previous sections followed this advice.
“The explanation of the ratio Bacteria:Moulds increasing with the vitiation of the air is that moulds come mostly from the outside air. When the air in a room becomes vitiated the bacteria increase largely, while the number of moulds is affected to a relatively much less extent, if at all.”“when a room is left quiet the micro-organisms settle out in a few hours, so that the air becomes comparatively free.”Fungi mostly come from outdoors, while bacteria are mostly emitted indoors. This is mostly consistent with findings iii, v, vi, and viii above.
“Hence it is clear that a certain amount of physical disturbance in a room is a condition necessary to the presence of micro-organisms in the air.”“The skin and clothes of the persons present in a room at the time of an observation also occur naturally as a probable source of infection of air.”Resuspension, as well as direct shedding from skin and clothes, are two main sources of indoor microbes. This is consistent with finding ix above. I should note that this study also found that the “cleanliness of rooms and persons habitually in them” affected airborne microbe counts. Higher “micro-organism counts” were found in homes that were classified as “very dirty” compared to “clean” upon visual inspection of both the house and its occupants.
“of the mechanically ventilated schools only two contained more than 26 micro-organisms per litre, whereas of the naturally ventilated schools only three contained less than 26 per litre.”(Note that there were a total of 18 mechanically ventilated schools and 28 naturally ventilated schools investigated for airborne microbes.)“The all-important argument for mechanical ventilation is that it maintains a certain standard of purity, and, unless some simpler method which will maintain a similar standard can be devised, its adoption in crowded schools seems to be very much required.”Building operation (including the source and rate of ventilation air delivery) impacts indoor microbes. This is consistent with finding x above (although these quantities of microbes are now known to be vastly underestimated).(Note that in this case “mechanically ventilated” meant that the schools were operated with dedicated outdoor air supply via mechanical means, and “naturally ventilated” meant that the schools were operated without mechanical means and primarily relied on infiltration [rather than open windows, despite the somewhat confusing use of a term that now refers to open-window ventilation]. In other words, the mechanically ventilated schools had higher ventilation rates [this was clear because carbonic acid concentrations {i.e., CO2 levels}] were higher in the naturally ventilated schools.)
“No constant relation between the quantities of carbonic acid, organic matter, and micro-organisms can be detected in individual cases.”“Sometimes we find a high organic matter accompanies by a low carbonic acid, whilst under other circumstances the reverse may be the case. A determination of carbonic acid alone is therefore never a sufficient indication of the purity or otherwise of a given sample of air.”The concentration of indoor microbes and built environment parameters are weakly correlated, if at all. This is consistent with finding xi above.