ON CHLOROCRUORIN. I

Summary. 1. Chlorocruorin, the red‐green pigment dissolved in the blood of certain polychaetes, exists in an oxidised and a reduced form, which have different absorption spectra. Chlorocruorin is a respiratory pigment in that the oxidised form can be reduced ( a ) by a vacuum, and ( b ) by living tissue, and then reoxidised by air. 2. Blood of Spirographis , containing chlorocruorin, gives off on the addition of potassium ferricyanide one‐third of the volume of gas given off by my own blood. 3. The absorption bands of oxychlorocruorin and reduced chlorocruorin resemble those of oxy‐ and reduced haemoglobin shifted towards the red end of the spectrum. 4. The oxychlorocruorin spectrum differs from that of oxyhaemoglobin in the relative heights of the a and β bands and in the presence of a third much smaller band. 5. Reduced chlorocruorin resembles the reduced haemoglobin of Arenicola in that the spectrum varies with the reducing agent employed. 6. The band of reduced chlorocruorin has a summit with a buttress on either side. Thus it differs from the simple summit of the mammalian and the double apex of the Arenicolan haemoglobin band. 7. The spectra of metachlorocruorin and chlorocruorohaematin differ considerably from those of methaemoglobin and haematin. 8. Chlorocruorochromogen closely resembles haemochromogen spectroscopic‐ally. The bands of the former are further towards the red than those of the latter, but the shift is less than in the case of oxy‐ and reduced chlorocruorin relative to oxy‐ and reduced haemoglobin. 9. The porphyrin prepared from chlorocruorin is either identical with haemato‐porphyrin or very closely resembles the latter. 10. Chlorocruoroporphyrin, like haematoporphyrin, has a brilliant red fluorescence.