IN a former paper'I have shown how by the examination of the fresh organs and tissues of Vertebrates and Invertebrates by means of the microspectroscope I was led to discover the presence of the histohaematins and of myohaematin; and I stated that I could not isolate these colouring matters unchanged. I was able to say that they are joined to proteids or that they are coloured proteids, and when isolated in the changed condition soluble only in water. In the present paper I can go further and show how they can be got into solution, and although as yet the pigmented portion cannot as in the case of haemoglobin be separated from the proteid constituent, yet one can definitely prove:(1) that a peculiar colouring matter is present in solution,(2) that it yields decomposition products which prove its near relationship to haemoglobin, while at the same time it fails to yield all such decomposition products, proving that it is distinct from haemoglobin or any of its decomposition products; and (3) one can form a fairly accurate idea as to the physiological r'ole which it may play and as to its reactions.

While I havenot yet succeeded in getting relatively large quantities of pigments so as to be able to deal with them analytically, yet the amount is sufficient for enabling me to prove their great importance from a physiological point of view. The proof of the existence of these colouring matters then rests no longer on the observation of the spectra of the fresh organs and tissues of animals, as I can now easily obtain coloured juiices from muscle, and from certain organs, in such quantity as to enable them to be dealt with in solution, and their reactions followed, by means of the spectroscope.