392 DISEASES OF UNCERTAIN ETIOLOGY 



Punioni, who has done recent work on this subject, concludes 

 thus : — 



The tissues which compose the cranium from the dura mater to the 

 skin, are diathermal both to the yellow-red and to the violet-ultraviolet 

 rays, but they absorb the red and green-blue rays. 



Sunstroke is brought about by the action of the violet-ultraviolet 

 rays upon the meninges and the cerebral substance. 



At the same time, one must not completely forget the red-yellow 

 rays, which facilitate the photo-chemical action of the violet-ultra- 

 violet rays by means of the heat which they produce. 



With regard to prophylaxis against sunstroke, it is well to protect 

 the susceptible parts (head, neck and spine) with green clothing, which 

 absorbs the violet-ultraviolet rays as well as the red-yellow, letting 

 pass the green rays only, which are harmless because they are arrested 

 altogether by the tissues of the cranium. 



Since in practice it is necessary to combine the prophylaxis against 

 sunstroke with that against heat stroke, it is advisable to cover the 

 green, heat-absorbing clothing with white material, which is well 

 known to possess the greatest reflecting properties. 



The eyes should be protected by means of coloured glasses; these 

 again, for the above reasons, should be green. 



SYMPTOMATOLOGY. 



The patients may be affected in various ways under different con- 

 ditions, thus : — 



(i) One may have been marching long in the sun, with tunic 



fastened up to the throat, when there are headache, convulsions, 



and not infrequently incontinence of urine. 



(2) Or the patient may perspire profusely, turn pallid with rapid 

 respirations and fall partly unconscious. 



(3) Or excessive thirst may be experienced followed by coma. 



(4) Or a headache may become more and more severe, with intoler- 

 ance to light; this may be followed by partial coma, with 

 recovery or death. If recovery there is often headache for six 

 or eight weeks. 



(5) Or after prolonged exposure to the sun, a hot dry skin, estab- 

 lished intolerance to light, sound and movement. 



There may be vomiting. 

 Recovery may be : — 

 (i) Sudden and complete. 



(2) Or prolonged over several days or weeks, then clearing up. 



(3) Or persisting and leaving some permanent trouble as impaired 

 memory, partial blindness or deafness, insanity, epilepsv. 



