Operatives who are exposed to irritating or poisonous gases and fumes, such as lead and its compounds, are likely to become victims of chronic poisoning. Gases that are merely irritating are of less importance than those that are poisonous, because irritating gases cannot be borne in large amounts and the person suffering from their effect is forced to seek the relief afforded by fresh air.

Offensive vapors and fumes, such as those given off in soap-making, glass-making, tanning, and rendering, etc., may cause general disturbance of the digestive system and headache for a time to those who are not used to their effects, but as a rule, tolerance is soon established and the odors are not even noticed. These odors are popularly regarded as leading to infectious disease, but this is not true, as they do not, in reality, undermine the human system.