INFLUENCE OF ROENTGEN RAYS UPON METABOLISM 891 



the eye. Those between 3.9 to 1.0 ten-thousandths of a millimeter con- 

 stitute ultra-violet light. Those exceeding 7.6 ten-thousandths of a milli- 

 meter in length are the infra-red waves. The ordinarily used unit of wave 

 length is the Angstrom unit, equal to one ten-millionth of a millimeter. 

 Another unit frequently used is the micron, |x = 0.001 mm. 



It is a general law of photochemical action that only those rays are 

 effective which are absorbed by the substance in which the reaction occurs. 

 Visible light rays are not as a general rule active but may be rendered 

 active by impregnating the tissue or other material with certain sub- 

 stances which in such cases act as the photochemical absorbent or senti- 

 tizer. Ultra-violet light rays are active as they are the easiest absorbed. 



Experience has shown that light can bring about a variety of chemical 

 changes. Neuberg(c) (d) (e) (/) (g} observed that the general effect of 

 light acting on organic substances present in animal and plant cells is to 

 produce from carbonyl containing materials aldehyds or ketone compounds, 

 whose reactivity and availability for important synthetic changes are con- 

 spicuous. These changes, however, could only be produced by the addition 

 of certain salts such as uranium, mercury, arsenic and manganese which 

 acted as photocatalytic agents. Neuberg and Schwarz have shown that iron 

 salts can act as photocatalyzers. They believe that in the presence of light 

 these photocatalyzers take oxygen from the air and pass it on to the 

 organic light receptors. This photocatalytic light action consists in oxida- 

 tion and cleavage processes. From their investigation they conclude that 

 sensitiveness to light is increased by giving mineral waters containing 

 heavy metals. Pincussohn ( c) has reported that a solution of sodium urate, 

 containing eosin, exposed to light shows a diminution in the content of uric 

 acid. The proteins of egg white and of the crystalline lens exposed to ultra- 

 violet light were found by Chalupechy to be considerably altered. The 

 albumins were decreased, the globulins increased and some coagulated 

 protein was formed. 



The action of light energy on tissues and skin has been studied quite 

 extensively. Bering sums up the work previous to 1914. He states that 

 the action of light manifests itself in cell destruction produced through 

 direct destruction or by edema and thrombosis as a result of a direct 

 action upon the endothelial membrane and musculature of the vessel wall. 

 There also results a hemorrhagic inflammation which terminates with a 

 productive connective tissue formation. The histological changes were 

 almost exclusively produced by ultra-violet light rays. The blue rays 

 possessed only a slight action and the green, yellow and red rays produced 

 no change. Sensitizing of tissues with substances such as eosin increased 

 the action of light but slightly. 



Schanz(a) has observed that light may alter the cell proteins, especially 

 in the presence of organic and inorganic substances such a silicates, sugar, 

 lactic acid and urea which act as sensitizers. The pyknosis and hyaline de- 



