I consider slaughtering within the City as both directly and indirectly prejudicial to the health of the population ;—directly, because it loads the air with effluvia of decomposing animal matter, not only in the vicinity of each slaughter-house, but likewise along the line of drainage which conveys away its washings and fluid filth; indirectly, because many very offensive and noxious trades are in close dependence on the slaughtering of cattle, and round about the original nuisance of the slaughter-house ... you invariably find established the concomitant and still more grievous nuisances of gut-spinning, tripe-dressing, bone boiling, tallow-melting, paunch-cooking, etc.
    Ready illustrations of this fact may be found in the gut-scraping sheds of Harrow Alley, adjoining Butchers’ Row, Aldgate; or in the Leadenhall skin-market, contiguous to the slaughtering places, where the stinking hides of cattle lie for many hours together, spread out over a large area of ground, waiting for sale, to the great offence of the neighbourhood.

Dr John Simon, City Medical Reports, 1849

see also Thomas Beames in The Rookeries of London - click here