376 RETROGRESSIVE CHANGES 



It is yery probable that not all of the effects of exposure to the sun 

 depend upon the heat rays, for there is evidence that the hght rays 

 may also produce effects. This is definitely true in the case of indi- 

 viduals or animals with certain pigments in their blood, notablj^ 

 hematoporphyrin (q. v.). In them, not only may skin eruptions re- 

 sult from relatively small exposure to light, but mice may be so sen- 

 sitized that a few moments of exposure to light is fatal. ^* Artificial 

 fluorescent substances, such as eosin, also sensitize tissues and proteins 

 to light. ^^ Normal blood absorbs light rays in large amounts, as 

 Finsen showed, and it is quite possible that changes in the chemistry 

 of the blood result from the light rays. Exposure to the sun may 

 cause a general leucocytosis with relative lymphocytosis.^^ 



According to HerteP^ the ultraviolet rays cause oxygen to spUt off 

 the easily oxidizable compounds of protoplasm, and Bovie*^ found 

 that they coagulate proteins; they also have a destructive effect on 

 enzymes, ^^ serum complement'*^ and hormones. ^^ However, Burge,^^ 

 found that exposure of living cells to ultraviolet radiation of sufficient 

 intensity to kill the cells does not decrease to any appreciable extent 

 the activity of the intracellular enzymes; the cell death he attributes 

 to coagulation of protoplasm. Harris and Hoyt^^ advance evidence 

 that the susceptibility of protoplasm to ultraviolet light is conditioned 

 by selective absorption of the toxic rays by the aromatic amino-acids 

 of the proteins. Toxins are reduced in activity by ultraviolet raj^s.^' 

 X=rays^^ stimulate cell growth when applied in small amounts,^^ 

 but larger amounts produce necrosis, which is peculiar in that an in- 

 terval of several days, or even weeks, may elapse after the exposure 

 before the necrosis manifests itself. Ellis^^ considers that the amount 

 of necrosis is out of proportion to the changes in the vessels, which 

 some have believed to be the cause of x-ray gangrene, and therefore 

 that the cells must be directly injured," a view supported by Case- 

 mir's^^ experiments with plant cells. The extensive studies of the 



" Hausmann, Biochem. Zeit., 1914 (67), 309. 



** Full review on photodynamic action of light by Sellards, Jour. Med. Res. 

 1918 (38), 293. 



« Aschenheim, Zeit. Kinderheilk., 1913 (9), 87; Taylor, Jour. E.\p. Med., 1919 

 (29), 41. 



*' Zeit. Augenheilk., 1911 (26), 393. 



*« Science, 1913 (37), 24; see also Burge, Amer. Jour. Physiol., 1916 (39), 335. 



" Brooks, Jour. Med. Res., 1918 (38), 345. 



60 Burge et al, Amer. Jour. Physiol., 1916 (40), 426. 



" Amer. Jour. Physiol., 1917 (43), 429. 



" Science, 1917 (46), 318; Univ. Caiif. Publ. (Pathol.), 1919 (2), 245. 



" Ilartoch et al, Zeit. Immunitat., 1914 (21), 643. 



** Full review by Colwell and Russ, "Radium, X-Rays and the Living Cell," 

 London, 1915. Also see Richards, Science, 1915 (42), 2S7. 



" See Schwarz, Munch, med. Woch., 1913 (GO), 2165. 



" Amer. Jour. Med. Sci., 1903 (125), 85. 



" Allen (Jour. Med. Research, 1903 (9), 462) states that protozoa ami vinegar 

 eels are killed by long exposure to a;-rays, whereas plants are dooiiledly stiinulatod 

 in their growth. 



" Med.-Naturw. Arch., 1910 (2), 423; rdsuni6 on a-rays. 



