G. H. F. Nuttall 
479 
Suited for such treatment are all the other articles enumerated under 
Steam. 
Effects of dry heat at various temperatures. The moderate degree of 
dry heat that is required for the destruction of lice and nits in clothing, 
blankets, leather, furs, etc., is insufficient to injure them. We have seen 
that an exposure to hot air at 60° C. for half an hour amply suffices to 
kill lice in all stages in practice. 
Hot air at higher temperatures exerts an injurious effect on woollens, 
thus 104° C. acting for 4 hours whilst but slightly yellowing white flannel, 
does not affect its tensile strength, but if exposed to f27° C. for half an 
horn flannel yellows and becomes brittle 1 . At high temperatures, hot 
air is liable to over-dry fabrics so that they become brittle, but if the 
heat is moderate this effect can be overcome by letting them reabsorb 
their usual amount of hygroscopic water from the atmosphere, this being 
accomplished in a short time by hanging them up freely exposed to the 
air. Leather will shrink and grow hard unless dried before exposure to 
hot air, it is unaffected by exposure to 60° C. for 1 hour (Uhlenhuth and 
Olbrich, 1915, p. 776) 2 . According to Kisskalt and Friedmann (1915, 
p. 398) furs are not injured by exposure to 80° C. for 30 minutes but they 
are damaged by repeated exposure to this temperature or by 78° C. 
acting for 2J hours. These authors recommend the use of electric fans 
in the heating chamber for rendering the temperature therein uniform 
when treating furs by hot air. Friedmann (1916, p. 321) states that sheep 
fur withstands dry heat much better than other furs. Seligmann and 
Sokolowsky (1915, p. 963) are wrong in asserting that temperatures of 
120-150° C. do not injure furs and leather. 
Relative advantages of Dry and Moist Heat. 
From the point of view of louse destruction alone, hot air has many 
advantages over moist heat, in that it can be applied to a greater variety 
of objects without injuring them, that a more moderate degree of heat 
can be applied at a smaller cost of fuel and apparatus, that it causes no 
shrinkage of fabrics and does not cause colours to run, that it does not 
remove the natural grease from woollens and render them hard to the 
touch, that it can be applied without injury to fur and leather (at 60° C.), 
1 Notter and Firth. (1908), Theory and Practice of Hygiene, London, Churchill, pp. 741 
et seq. 
2 Konrich (1912, zur Desinfektion von Lederwaren und Buchern durch heisse Luft, 
Zeitschr. f. Hyg. lxxi. 296-306) exposed books and leather equipments (military) to hot 
air at 80° C. for 24 hours, he claims without injury. I suspect that the leather deteriorated. 
