THE EXTERNAL ENVIRONMENT 257 



an electric field is not favourable to the organism, and can at 

 length compromise the health. The effects of lightning are 

 familiar, but it is interesting to note that the liability to be struck 

 by lightning seems to vary with different trees. The effects 

 on human beings are terrible. For instance, two labourers 

 were hit in a field ; one died on the spot, the other survived but 

 a few hours ; their clothes were burnt ; the skull was broken as 

 by a stroke of a club ; often the man who is hit is thrown some 

 distance. 



Prevost and Batelli (*) have shown that an alternating current 

 of low tension stops the heart, but the respiration continues for 

 a few minutes ; at average tensions both stop ; at high tension 

 the current stops the respiration but the heart continues to beat. 

 In these conditions artificial respiration is indicated. An 

 alternating current is much more dangerous for equal voltages 

 than a continuous current. 



Severe shocks ( 2 ) can cause stoppage of the heart and anaemia 

 of the nervous centres ; or, by paralysing the respiratory organs 

 produce asphyxiation ; in this case especially artificial respiration 

 is of use. 



A statistic of 55 fatal accidents caused by electricity in mines 

 has shown that 53 of them, that is, 96%, are due to defective 

 insulation of cables and bad earth connexions. 



The effects of a magnetic field are obscure and doubtful. 

 Schiff could observe no effect on the muscles and the neives 

 when exposed to a magnetic field in any direction. ( 3 ) Peterson 

 and Kennely ( 4 ) operating in Edison's laboratory with very 

 powerful electro magnets, could perceive no action on a normal 

 man. Lord Lindsay and Cromwell Varley found that there was 

 no effect whatever when the head of a man was placed between 

 two magnetic poles. 



At the same time Fere ( 5 ), by means of an ergograph, found 

 an increase of muscular force in an arm when brought within 

 a distance of 1 metre from a magnet ; while in the other arm the 

 force diminished. Finally, Danilewski and Grandis ( 6 ) claim that 

 magnetic field can excite the muscles if its lines of force act per- 

 pendicularly to the fibres. This phenomenon is contested, and 

 in any case diversely interpreted. 

 



(*) Provost and Battelli (Journ. de PhysioL, 1899, 1900). G. Weiss 

 Bull. Soc. Intern, des Elect., 3rd Series, vol. i., No. 8, 1912. Gerbis (Elektr. 

 Zeitsch., July, 1913). 



( 2 ) Electrician, 7th April, 1911. For accidents due to electric shock see 

 Langlois (Rev. Gen. Sc., April, 1913). 



( s ) Schiff (Arch. Sc. Phys. et Nat., 1888, 3rd Series, i.). 



() Peterson and Kennely (New. York Med. Jouru, 31st Dec., 1892). 



( 6 ) Fer6 (Comptes Rendus Biologie, 1902, pp. 388, 509). 



() Grandis (Arch. I tat. Biol., 1902, vol. xxxvii., p. 313). 



