BIOLOGICAL ACTION OF LIGHT HILL 329 



(1 in 40,000 solution) in a quartz container absorbs rays shorter than 

 306 fjiix (Dhere). The mercury-vapor Lamp through this screen pro- 

 duces no erythema even after giving six times the erythema dose for 

 the unscreened lamp. Lines 275 and 257 /x/a of the cadmium spark 

 spectrum produce erythema, but not line 232 fj^ix. Such short rays 

 do not penetrate the horny skin but actively kill infusoria.^ 



How slight is the penetrating power of the ultra-violet tsljs is 

 shown by interposing in place of the quinine solution a thin fdm of 

 the horny layer of the skin taken off a blister, or the mesentery of a 

 rabbit. Such a film protects the skin no less that the solution of 

 quinine. 



The active ultra-violet rays penetrate to the deeper epidermic cells 

 but no farther. Among these cells there takes place multiplication 

 and growth, formation of pigment and transition into the horn}^ 

 material, which is pushed outwards by the growth of cells within 

 In these cells the ultra-violet rays provoke changes which we may 

 assume are similar to those which have been photographed in living 

 anthrax bacilli by Mr. J. E. Barnard, using a microscope with quartz 

 lenses and a band of ultra-violet rays from the cadmium spark. 

 Under the ordinary microscope they have been observed by A. Eidi- 

 now and L. Hill on infusoria. An increasing aggregation of parti- 

 cles takes place in the bioplasm; in the case of infusoria this leads 

 to cessation of movement, death, rupture, and setting free of the 

 particles. So, too, the surface film of egg white exposed in a quartz 

 chamber is coagulated by ultra-violet rays. Positive particles are 

 dispersed and negative ones aggregated (Clark). 



These rays displace electrons in atoms according to present ph} si- 

 cal theory and so alter the charge of the particles, some of which 

 are to be seen in bioplasm by dark ground illumination and high 

 microscopic magnification in active Brownian movement. This 

 leads to aggregation started by the displacement of electrons in 

 the atoms. Chemical change in molecular structure ensuing in the 

 epidermal cells after a latent period, reaches such an irritative na- 

 tiu-e as to lead to dilatation of the subcutaneous blood vessels, exuda- 

 tion of lymph, increase of lymphocytes, and rise in the hsemobac- 

 tericidal power of the blood. In cases of rickets the abnormally 

 low inorganic phosphorus content of the blood which is significant 

 of this condition is put up also in a striking way. Subsequent to 

 these reactions there results desquamation, due to death of some 

 epidermal cells followed by pigmentation. The pigment melanin 

 is laid down as granules in that layer of living cells which lies close 

 underneath the horny layer. Melanin is stated to be formed by the 

 action of an oxydase in the deeper epidermic cells, as may be seen 



" I am indebted to Messrs. J. E. Barnard and J. Smiles for the use of the spark. 



