256 THE HUMAN MOTOR 



coloured screens, von Schrotter f 1 ) proved that it is the portion 

 of the spectrum from blue to ultra-violet, which produces 

 cutaneous erythemia, and this action is very marked at great 

 altitudes. 



Negroes are less exposed to this disease than white races, 

 because their pigment changes the chemical rays into calorific 

 rays ; " the negro lives in the shelter of his skin " (Ch. Ed. 

 Guillaume). 



Solar light, when it is mild, favours visual acuteness, the 

 perception of colours, and a clear view of details. When it is 

 intense, which is the case, for instance, in the Mediterranean 

 countries, it provokes ocular diseases, and a slight deformation 

 of the ball of the eye (inverse astigmatism), which is rare in 

 Northern countries. ( 2 ) 



The solar heat,( 3 ) in the tropics can raise the temperature of 

 the human skin from 3 to 4. It has been observed that, in these 

 circumstances, negroes perspire enormously to counteract 

 hyperthermia. 



In short, owing to its heat and its chemical radiations intense 

 sunlight is a danger to man and animals. 



The units of light, photometry and the lighting of workshops 

 will not be discussed here. They are essentially matters oi 

 industrial hygiene. 



189. Influence of Electric and Magnetic Fields. The sun, 

 thunderstorms, and industrial electric machinery pour into the 

 atmosphere a prodigious quantity of electrified particles called 

 ions. The ionisation of the air is a permanent phenomenon, 

 which has no effect on man. It is not known whether or not it 

 increases his muscular force and his expenditure of energy. 



The electric current excites the muscles and the nerves by 

 acting locally as a shock ; the application of a moderate current 

 appears to increase the power of the muscles, an effect which 

 lasts for several days. ( 4 ) The action of an electrified environment 

 as after a violent thunaerstorm, or in a radiotelegraphic station, 

 produces a reverse effect, a slight depression of the nervous 

 system, anaemia and a sort of apathy. Is this due to the elec- 

 trification of the air or to the presence of ozone ? It has been 

 found that ozone has microbicide. cellulocide,( 5 ) and probably 

 nervous ( 6 ) effects. One might therefore say that the effect of 



(*) Mission to Teneriffe, Jean Mascart (loc. cit.). 



( 2 ) Jules Amar (Journal de Physiologic, 1908, pp. 231-7). 



( 8 ) Hans Aron Philippine Journal of Science, vol. vi., April 1911). 



( 4 ) Capriati (Riv. Sper. di Frenol. e Med. Leg., vol. xxvii., p. 285, 1901). 



( 6 ) Candiotti (Revue Gen des Sciences, 1911, p. 224). 



() Elektrotech. Zeitsch. of 17th April, 1913. 



