JOHN F. NORTON 377 



are various reports concerning the effect of exposure of animals to ultra-violet rays on 

 their ability to produce antibodies.' On the whole, however, the results obtained are 

 quite inconclusive. In view of the present furor over heliotherapy, investigations 

 along this line might prove fruitful. 



THEORETICAL 



Finally, we may profitably ask. What is the mechanism by which ultra-violet 

 rays of wave-lengths between 3,000 and 1,850 A exert such rapid action on bacteria? 

 That the presence of free oxygen is essential for the photogermicidal action was dis- 

 proved many years ago and has already been referred to. Fair^ believes that the for- 

 mation of hydrogen peroxide cannot account for the effects produced. That the ac- 

 tion of light-rays is directly on or in the cell is now generally admitted. However, it 

 should be emphasized that in the presence of certain substances there is a marked pro- 

 tection. ^ An alkaline reaction in the medium, inorganic salts and aromatic organic 

 compounds are examples of this. Dreyer,^ on the other hand, claims to have sensitized 

 bacteria by dyeing with erythrosin. The evidence that bacterial protoplasm and 

 many proteins will absorb ultra-violet rays is indisputable, and the facts concerning 

 lipoids are well known. I think we can safely assume a direct photochemical action 

 on the bacterial cell. But this is hardly a satisfying explanation. What happens 

 when bacterial protoplasm absorbs the rays? Both inorganic and organic colloids 

 undergo changes as a result of exposure to ultra-violet light. These changes are ac- 

 companied, perhaps preceded by, change in the electrical charges on the particles. 

 Bacteria, being charged particles, might be first affected in this way. Mrs. Clark^ has 

 developed a photo-electrical theory postulating that electronsaregiven off from proteins 

 under the action of ultra-violet rays and that these electrons attach themselves to other 

 atoms or molecules with the resulting changes in both physical and chemical properties 

 of all substances concerned. For instance, coagulations of proteins may follow ex- 

 posure to light-rays. Many disinfecting agents are protein coagulants and may de- 

 pend on this property for their germicidal action. Ultra-violet light would, on this 

 basis, be an agent comparable with known chemical disinfectants. Fair^ states that 

 the disinfection curve suggests that the action is similar to that of other germicidal 

 agents. 



The destruction of bacterial cells by means of ultra-violet light offers an attrac- 

 tive opportunity for the study of the mechanism of disinfection since the action takes 

 place without the addition of extraneous chemical substances. Intensive research in 

 this field is much needed and is likely to be productive of significant results. 



' Pincussen, L.: loc. cit.; Potthoff, P., and Heuer, G.: Centralbl.f. Bakteriol., Abt. I, 88, 299 

 1922; Hansen, T.: Ada. med. Scatidinav., 56, 629. 1922. 

 2 Fair, G. M.: J.A.W.W.A., 7, 325. 1920. 

 s Houghton, E. M., and Davis, L.: Am. J. Pub. Health, 4, 224. 1914. 



"Ellis, C, and Wells, A. A.: The Chemical Action of Ultraviolet Rays, p. 244. Chemical Catalog 

 Co., 1925. 



s Clark, J. H.: Physiol. Rev., 2, 277. 1923. ^ Fair, G. M.: loc. cit. 



