64 A MANUAL OF PHYSIOLOGY 



a considerable time. Examine some of the blood (after dilution) 

 with the spectroscope. Two bands, almost in the position of the 

 oxyhaemoglobin bands, are seen ; but no change is caused by the 

 addition of ammonium sulphide, since carbonic oxide haemoglobin 

 is a more stable compound than oxyhaemoglobin. 



(d] Methamoglobin. Put some blood into a test-tube, add a few 

 drops of a solution of ferricyanide of potassium, and heat gently. On 

 diluting, a well-marked band will be seen in the red. On addition 

 of ammonium sulphide this band disappears ; the oxyhaemoglobin 

 bands are seen for a moment, and then give place to the band of 

 reduced haemoglobin (Fig. 8). 



(e) Acid Htzmatin. To a little diluted blood add strong acetic 

 acid and heat gently. The colour becomes brownish. The spectrum 

 shows a band in the red between C and D, not far from the position 

 of the band of methaemoglobin. The addition of a drop or two of 

 ammonium sulphide causes no change in the spectrum, and this is a 

 means of distinguishing acid-haematin from methaemoglobin. If 

 more ammonium sulphide be added, haematin will be precipitated 

 when the acid solution has been rendered neutral, and a further 

 addition of ammonium sulphide or sodium hydrate will cause the 

 haematin to be again dissolved, a solution of alkaline haematin being 

 formed. This in its turn may be reduced by an excess of ammonium 

 sulphide, and the spectrum of haemochromogen may be obtained 

 (Fig. 8). 



(/) Alkaline Hcematin. To diluted blood add strong acetic acid 

 and warm gently for a few minutes. Then, when the spectroscopic 

 examination of a sample shows that acid-haematin has been formed, 

 neutralize with sodium hydrate. A brownish precipitate of hsematin 

 is thrown down, which dissolves in an excess of sodium hydrate, 

 giving a solution of alkaline haematin. 



Or add sodium hydrate to blood directly, and warm for a couple 

 of minutes after the colour has changed decidedly to brownish- 

 black. The spectrum of alkaline haematin is a broad but ill-defined 

 band just overlapping the D line, and situated chiefly to the red side 

 of it (Fig. 8). 



() Hcemochromogen. To a solution of alkaline haematin add a 

 drop or two of ammonium sulphide. The band near D disappears, 

 and two bands make their appearance in the green (Fig. 8). 



(h) Hcematoporphyrin. Put some strong sulphuric acid in a test- 

 tube. Add a few drops of blood, agitate the test-tube till the blood 

 dissolves, and examine the purple liquid, diluting it, if necessary, with 

 sulphuric acid. Its spectrum shows two well-marked bands, one just 

 to the left of D, and the other midway between D and E (Fig. 8). 



(3) Guaiacum Test for Blood. A test for blood much used in 

 hospitals, and, indeed, a delicate one, but noi always trustworthy 

 unless certain precautions be taken is the guaiacum test. A drop 

 of freshly-prepared tincture of guaiacum is added to the liquid to be 

 tested, and then ozonic ether (peroxide of hydrogen). If blood be 

 present, the guaiacum strikes a blue colour. The decomposition ot 

 the peroxide by the blood seems to be due to the stroma of the cor- 



