PHOTODYNAMIC ACTION 715 



phylloerythrin excretion. Chief among these diseases of uncertain eti- 

 ology are trefoil dermatitis, associated with various species of Trifolium 

 and Medicago species (Hurst, 19-1:2) ; rape scald, seen occasionally in sheep 

 grazing on Brassica rapa (Cunningham et al., 1942); and Erodium photo- 

 sensitivity, caused by Erodium cicutarium (Hurst, 1942), and E. mos- 

 chatum (Clare, unpubhshed observations). 



PHOTODYNAMIC ACTION IN HUMAN AILMENTS 



It is necessary to preface the following references to human diseases 

 with a reminder that photodynamic action is not synonymous with 

 photosensitivity. The triple response to blue and violet hght (Blum, 

 1941a) and the sensitivity shown by some persons after sulfanilamide 

 therapy (Blum, 1941b) are two examples which have been shown to be 

 independent of molecular oxygen and which therefore do not fall within 

 the definition of photodynamic action. (It is quite possible that similar 

 sensitivities occur in lower animals also, hut such rare reactions of indi- 

 viduals would be less noticeable among animals and not likely to be the 

 subject of specialized investigation.) 



Those reactions of human beings to light which do appear to be due to 

 photodynamic action are generally of the type defined as primary in the 

 section on animal diseases. The one possible example of Type II is the 

 photoreaction associated with certain forms of porphyria, but, as will be 

 indicated later, the etiology of these lesions is extremely doubtful. There 

 is no evidence of hepatogenous photosensitivity occurring in human 

 beings, and since the chlorophyll content of the human diet is com- 

 paratively low and the conditions of the human digestive tract are not so 

 favorable to phylloerythrin formation as those in the ruminant stomach, 

 this type of photosensitivity is scarcely to be expected. 



Photosensitivity Following Medication with Dyes. According to Blum 

 (1941a), accidental photosensitization has resulted from therapeutic use 

 of eosin (in epilepsy), trypofiavine (for gonorrhea), and hematoporphyrin 

 (for melanchoHa) and after injection of rose bengale as a test for hver 

 function. 



Photosensitivity Due to Contact. There have been a number of reports 

 of photosensitivity through contact of the skin with fluorescent sub- 

 stances or materials containing them. Blum (1941a) cites instances 

 attributed to contact with grass, figs, parsnip, perfumes containing ber- 

 gamot or citron oils, green soap, and coal-tar and petroleum derivatives. 

 Most of these materials contain fluorescent substances such as chloro- 

 phyll, coumarin derivatives, and acridine compounds which might have 

 produced the effects provided conditions were favorable for penetration 

 through the corneum. The need for light to elicit the effects has been 

 demonstrated in some cases, and definition of action spectra has been 



