58 APPLIED PHYSIOLOGY 



Wool is therefore a better non-conductor than either 

 vegetable fibre or silk. 



Equally important, however, to the material em- 

 ployed is the mode in which it is woven ; for the air 

 enclosed between the different layers of clothing, and 

 entangled in its meshes, forms a warm envelope which 

 is a worse conductor of heat than any material of which 

 clothes are made, and which greatly interferes with 

 heat loss, besides being not readily removed even by 

 convection. Thus, too, garments which enclose a layer 

 of air between them are much more efficient in checking 

 loss than one garment, even though it be equal in 

 thickness to two. Clothes should therefore fit loosely. 

 They should also be loosely woven, so as to enclose as 

 much air as possible in the interstices of the material. 

 Here again the superiority of woollen garments is pro- 

 nounced, for 1,000 volumes of soft flannel contain 

 923 volumes of air, as against 723 contained in linen. 

 It is in accordance with this principle that * cellular ' 

 clothing is made.* 



The utility of clothes is greatly interfered with by 

 damp, for the moist air penetrates into the interstices 

 of the cloth and removes heat from the body by evapora- 

 tion. Wet clothes, indeed, are almost worse than none, 

 for they greatly increase loss by evaporation. Thus, it 

 has been calculated that, if the boots and stockings are 

 thoroughly wet and allowed to dry on the feet, they 

 remove as much heat as would have been required to 



* It is noteworthy, too, that even in the lower animals the hair 

 stands on end in extreme cold, so as to enclose as large an amount 

 of air as possible. The production of ' goose-flesh ' in the human 

 subject is apparently a survival of the same device. 



