PLATE I.

Spectra (after Neubauer and Vogel).

1. a, Oxyhemoglobin; 6, hemoglobin free from oxygen.

2. Methemoglobin: a, in neutral solution; b, in alkaline solution. 3. a, Hematin in acid alcoholic solution; b, in ammoniacal solution; reduced hematin.

4. a, Urobilin in acid solution; b, zinc salt in ammoniacal solution.

water, and adding the resultant mixture to 6 parts of ammonia and filtering.

Carbon-monoxid Hemoglobin.-Attach a piece of rubber tubing to a gas-tap, and provide this with a small piece of glass tube sufficiently long to reach to the bottom of a test-tube. With the aid of this tube pass a slow current of coal-gas through the blood solution. Note the change to a bright cherry red in the color of the blood. Examine the spectrum of this solution. Two bands appear, which are situated very near the bands of oxyhemoglobin. Compare with a similar solution of fresh blood. It will be found that the bands of carbon-monoxid hemoglobin are fainter and less well defined. On careful examination with a spectroscope with a scale attached, it will be seen that the bands are somewhat nearer the violet end of the spectrum than are those of oxyhemoglobin.

Treat the solution of carbon-monoxid hemoglobin with ammonium sulphid. Examine the solution with the spectroscope. Note that the spectrum remains unchanged. Carbon-monoxid hemoglobin is not affected by reducing agents.

To 10 c. c. of carbon-monoxid hemoglobin solution add an equal volume of sodium hydroxid solution. Note the bright appearance of the mixture. Treat a solution of oxyhemoglobin in the same way. Observe the appearance of a dirty-brown precipitate or coloration.

Methemoglobin.-Methemoglobin is an oxidation-product of oxyhemoglobin. It is produced by the action of weak oxidizing agents such as potas

sium ferricyanid. It is found in the blood in cases of poisoning by strong oxidizing agents, such as potassium chlorate.

To a concentrated solution of blood add a few drops of a freshly made solution of potassium ferricyanid. Allow to stand for some minutes, and note the change in color to a brownish tint. Examine the diluted solution with the spectroscope. The spectrum is especially characteristic. Almost complete absorption takes place in the blue region of the solar spectrum. A narrow band will be found near the position of the narrower oxyhemoglobin band, and a well-marked band occurs toward the red end of the spectrum.

Alkaline Hematin.-Solutions of alkaline hematin are prepared by heating blood-pigment with alkalies. The hemoglobins break up under this treatment, yielding a hematin-pigment and an albumin. When oxyhemoglobin is treated in this way the compound hematin results. When hemoglobin is boiled with alkalies in the absence of air, reduced hematin results.

Heat 10 c. c. of blood solution with 1 c. c. of sodium hydroxid. The color of the solution changes to a brownish green. The spectrum of this solution is not characteristic; complete absorption takes place in a part of the red spectrum. If this solution be reduced with yellow ammonium sulfid or with Stokes' reagent, one obtains the spectrum of reduced hematin or hemochromogen. The spectrum of this compound is 'scarcely to be distinguished from that of oxyhemo