238 THE HUMAN MOTOR 



The mode of operation will be seen later. In spinning mills, 

 where there is always great moisture, a skein of wool is placed 

 in the scales ; the heavier it is the greater the humidity. The 

 working of textiles reqyires a humid atmosphere which is arti- 

 ficially maintained. Here are some examples 01 the humidity 

 maintained in cotton irills: 



Preparing room e 



Combing ,, 



Carding 55 to 60 



Finishing , 65 to 70 



Cotton weaving 75 to 80 



Spinning and weaving of linen, jute, hemp 80 to 85 



Spinning of silk 70 to 75 



Spinning and weaving of wool 80 to 90 



It will be seen that very often the air of these mills is almost 

 saturated. 



174. Perspiration. Rubner ( x ) made the best researches on this 

 question. Conformably to the idea of physical equilibrium, he 

 recognised that the pulmonary and cutaneous evaporation in- 

 creases with the state of dryness of the atmosphere. It becomes 

 almost double when there are 5 grammes of water vapour instead 

 of 9 in one cubic metre of air. In short, the value of the elimina- 

 tion of water vapour by the organism varies inversely with the 

 hygrometric state. It is the same with fasting or fed subjects, 

 but the elimination is more rapid in the case of overfeeding. 



Comparing the influence of the hygrometric state with that 

 of the temperature, Rubner shows that- all things being equal 

 the temperature increases the emission of water ; the minimum 

 takes place between 10 and 15 C., while from 25 C. onwards 

 the emission is rapid. Wolpert finds a minimum at about 18 

 and a maximum at 37 C. 



An analogous phenomenon has been found amongst vegetables, 

 especially in those which grow in the desert and are called 

 xerophytes (from x P? dry). The perspiration of plants is 

 more intense in the sun than in the shade, because of the ab- 

 sorption of red rays, which are calorific, while it can be stopped 

 by a saturated environment. 



In man and animals, the emission of water vapour appears to 

 be a complex physical and physiological phenomenon, subject, 

 undoubtedly to the action of the nervous centres. The r61e of 

 these centres is to regulate the perspiration so as to adapt it to 



( l ) Max Rubner (Arch, f Hygiene, vol xvi., p. 101, 1892). H. Wolpert 

 (Ibid., vol. xxvi., p. 32, 1896 ; vol. xxxiii., p. 206, 1898) ; Wolpert and 

 Broden (Ibid., vol. xxxix., p. 208, 1901) may also be consulted. 



