PHOTODYNAMIC ACTION 709 



photosensitization on oral administration to guinea pigs. Little is known 

 of the constitution of these compounds, but Wender et al. suggest, from 

 comparison of absorption spectra, that they may be related to the 

 hypericins. The absorption spectra of the buckwheat pigments isolated 

 by Wender et al. are consistent with observations on the action spectrum 

 for fagopyrism made by Sheard et al. (1928), Mathews (1938), and Chick 

 and EUinger (1941). 



Photosensitized Keratitis in Calves Dosed with Phenothiazine. An 

 unusual form of photosensitivity which also falls within the primary 

 type is the keratitis, or corneal opacity, which occurs in calves dosed 

 with phenothiazine (as an anthelmintic) and then exposed to sunlight 

 (Whitten et al., 1946). Sheep are not affected unless large amounts of 

 phenothiazine are given. Clare (1947) found that in both calves and 

 sheep the sulfoxide derivative of phenothiazine is absorbed from the 

 digestive tract and converted to phenothiazone, but in calves this con- 

 version is incomplete, so that phenothiazine sulfoxide passes to the sys- 

 temic circulation and hence to the aqueous humor. Phenothiazone, 

 however, probably because it is conjugated as an ethereal sulfate, does 

 not reach the corneal tissues. Phenothiazine sulfoxide was found in 

 aqueous humor of affected calves and produced keratitis when injected 

 into the anterior chamber of the eye of an undosed animal exposed to 

 light. The action spectrum in these experiments was limited to the 

 narrow range of wave lengths (up to 3600 A) corresponding to the 

 absorption spectrum of phenothiazine sulfoxide (Clare et al., 1947). 



There have been reports (Thorning et al., 1942; Swales et al., 1942; 

 Britton, 1943) of photosensitivity of white skin and keratitis following 

 administration of phenothiazine to pigs, another species in which pheno- 

 thiazine sulfoxide is found in the peripheral blood (Clare, 1947). It is 

 possible, however, that the phenothiazone contributes to the skin lesions 

 in such cases, since even sheep will show a photoreaction of the skin if 

 the skin is shaved and exposed to intense light (ibid.). 



Apart from this hazard in the use of phenothiazine in calves and pigs, 

 there appear to be no other reports of photosensitivity in domestic ani- 

 mals following medication with fluorescent substances. 



Other Photosensitivities of the Primary Type. The photosensitization of 

 rats and guinea pigs by pigments in dried Panicum miliaceum has been 

 discussed earlier in this chapter, and since it has not been demonstrated 

 in domestic animals, it need not be considered further here. Many other 

 plants have been accused of causing photosensitivity, sometimes on 

 sound, but often on slender, evidence. Because there is so httle known 

 of them, these cases will be referred to in an unclassified group later in 

 this review. Nevertheless it is very probable that many of these diseases 

 are of the primary type, especially some of the better known ones such as 

 trefoil dermatitis, rape scald, and Erodium photosensitivity. 



