covery of which threw light on the chemistry of this important animal substance. Hoppe-Seyler's main work, however, to which we may direct attention, was done upon the red pigment or hæmoglobin of the blood, upon processes of oxidation in the organism, upon the chemistry of fermentation, and upon chlorophyll.
It is not too much to say that if all work but Hoppe-Seyler's upon hæmoglobin should be obliterated, we would still have nearly all that is known of that important substance. It was Hoppe-Seyler who gave the name hæmoglobin, it was he who discovered that it was this substance in the red blood-corpuscles that gave them their power of carrying oxygen, and that hæmoglobin was a definite chemical compound. He discovered the difference between hæmoglobin and oxyhæmoglobin. The absorption bands in the spectra and the difference in the spectra of hæmoglobin and oxyhæmoglobin were also discovered by him, and he did more than any other one man to apply the spectroscope to the study of the blood pigment. It was Hoppe-Seyler who found that the oxygen combined with and was given up from the hæmoglobin in a molecular and not an atomic form; he showed that carbonic oxide enters into a stable combination with hæmoglobin, and thus explained the peculiarly poisonous nature of this gas. He discovered and named the decomposition products of hæmoglobin, methæmoglobin, and hæmochromogen. He showed that hæmin was simply the hydrochlorate of hæmatin, and pointed out how the hæmoglobin molecule could be taken to pieces and built up by reduction. On the chemistry of hæmoglobin he published no less than thirty papers.
An interesting discovery made by him was the cause of the sudden death to which men were subject who, after working under compressed air, suddenly returned to the ordinary atmosphere. He showed that under such circumstances the dissolved gases of the blood quickly escaped from solution with fatal results. This discovery indicated the proper manner of avoiding such disaster by a gradual return to the normal atmosphere, and has been the means of saving many lives.
One of the greatest discoveries of Hoppe-Seyler was that the tissues and not the blood are the seat of the oxidations of the body. This was still more convincingly shown later by Pflüger. By this discovery Hoppe-Seyler's attention was attracted to the respiration of protoplasm, with what results we shall shortly see.
His work on hæmoglobin led Hoppe-Seyler in two directions: one was toward the composition of cells, the other toward respiration. Both paths have been followed with good results. In examining the composition of the red blood-corpuscles of mammals, Hoppe-Seyler discovered that the percentage of phosphoric acid contained in the
