The chief pigment of normal urine is known as urobilin (seeing that this name indicates a relation to “bile,” “urochrome” would be a better term, not connoting any view as to genetic relationship). The name for the chromogen “urobilinogen” would become “urochromogen.” Other pigments are or may be present in normal urine, e.g., the indigo-blue pigment whose ancestor is intestinal indol, and “uroerythim” genetically related, it is believed, to skatol, while, according to some physiologists, traces of “pathological urobilin” (which, might be better called para-urochrome) and even of hæmatoporphyrin are recognisable in healthy urine.

Certainly, in some morbid urines, urohæmatoporphyrin has been the chief pigment replacing urobilin, while, in a few very rare ones, a pigment allied to it, but, according to M'Munn, less de-oxidised, has appeared. This substance, like urobilin and urohæmatoporphyrin, is a proteid-free, iron-free pigment, as yet unnamed. I propose to call it meio-de-oxyhæmatoporphyrin. Urobilin is amber-coloured, urohæmatoporphyrin makes the urine of orange tint, while the rarer ally gives it a deep port-wine colour: urines containing this last do not decompose for many weeks.

I lately encountered meio-de-oxyhæmatoporphyrin in the urine from a case of rare skin-disease, Dermatitis herpetiformis bullosa. Both these hæmatoporphyrins have absorption-spectra resembling that of alkaline hæmatoporphyrin, and each, on the addition of strong sulphuric acid, is changed to the characteristic two-banded acid-hæmatoporphyrin.