So with the vapour which arises from an overcrowded and even from any churchyard. People who are accustomed to reside near badly regulated graveyards are mostly unable to detect the serious nuisance by the sense of smell; but medical men, accustomed to the dissecting-room, can recognise it directly, and can even distinguish it from the foul odours arising from sewers. In a case at Manchester, where a main sewer ran through the graveyard, the graves drained into it, and the smell of the dead came into the houses through the untrapped sinks. Mr. Roe stated on oath that he once traced exudation from a churchyard in St. Pancras parish into the road-sewer thirty feet distant, and that this would have resulted even if the sewer had been cemented or concreted over. These cases will prove that there are more sources of danger than from surface-emanations. The rule seems to be that, where the graveyards and roads are paved, and the stones laid horizontally, the escape of the deleterious matter is either into the wells or sewers. If, as in many instances, the surface of the burial-ground be above that of the street, the loathsome matter may even be seen trickling down the walls of enclosure. Some most sickening cases were published in 1851 in the report issued by the General Board of Health. If the formation of a deep sewer will suffice to drain dry all the wells near its line of march, then the sinking of a well near a burial-ground must help to drain the latter. There is a complication when drains in the neighbourhood of graveyards are tide-locked at intervals; and an instance of this was given by Dr. Reid, who stated that careful examination of the air in the Houses of Parliament, thirty years ago, resulted in the discovery that it was very much vitiated, both by night and by day, from their proximity to St. Margaret's burial-ground.