Moisture almost invariably favours the growth of bacteria, but some species can exist for a lengthened period in a dry medium. Sunlight, on the other hand, retards the growth of bacteria, and is often positively fatal to them, particularly in the presence of oxygen. Sunlight and fresh air are, therefore, the natural germicidal agents which the practical sanitarian must endeavour to utilise to the best advantage. It is also essential that rooms containing sanitary fittings should be so constructed and arranged that they can be kept scrupulously clean with the least possible trouble. Accumulations of dirt or dust in dark, unventilated rooms generally constitute suitable soils for the growth of bacteria.

A so-called "sanitary fitting" which requires the constant use of some chemical disinfectant or deodorant to keep it "sweet," is radically defective. An exception may be made in the case of urinals, which are notoriously the most evil-smelling of all sanitary fittings. A simple deodorant is there often of service. Disinfectants, however, are only required in special cases of sickness, and do not fall within the province of this work.

Foul Air

Disease germs are not the only evils to be guarded against. The foul air arising from defective sanitary fittings, drains, and sewers, may be comparatively free from germs, but may nevertheless be injurious to health if continuously respired. It is therefore necessary to exclude such air as much as possible from our buildings, or, if it is unavoidably produced within the buildings, to remove it without delay by proper ventilating appliances.