The pigment responsible for the photosensitivity in geeldikkop and also that developing after operative ligature of the bile duct in sheep (experimental icterus) has been isolated and identified as phylloerythrin, a porphyrin derived form chlorophyll. In the absence of chlorophyll from the diet, experimental animals neither became photosensitive nor could phylloerythrin be isolated from the bile, serum or faeces. The agencies responsible for the biological transformation of chlorophyll into phylloerythrin in the sheep are under investigation. Preliminary results show that the phylloerythrin is formed in the fore-stomachs and is probably a product of protozoal or bacterial activity. The icterogenic factor in geeldikkop is still under investigation.
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