356 APPLIED SCIENCE 



401. Perspiration. Perspiration consists of water 

 charged with waste products. This water is evaporated 

 from the skin by the air. If the air is saturated with moisture, 

 as it often is during the summer, water does not evaporate 

 quickly and consequently perspiration does not evaporate at 

 its usual rate. As a result we sweat or perspire very freely. 

 When we fan ourselves we create a small breeze which quickly 

 evaporates or absorbs the perspiration. 



Moisture is, however, readily taken up by dry air, and a 

 consequent cooling results. But if the atmosphere has a 

 humidity of 100 per cent, as it has just before or after rain, 

 the perspiration cannot be evaporated since the air already 

 has all the moisture it can hold. Everyone has noticed that 

 when the sun shines on a hot day just after a rainfall, the 

 heat is almost unbearable. 



402. Noxious Gases. Operatives who are exposed to 

 irritating or poisonous gases and fumes, such as lead and its 

 compounds, are likely to become victims of chronic poison- 

 ing. Gases that are merely irritating are of less import- 

 ance 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 head- 

 ache 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. 



