CH. X.] HAEMIN. 249 



spectroscopically., after suitable dilutions, shows a four-banded 

 spectrum. The centres of the bands are at X 622, X 576, X 539 and 

 X 504 approximately. 



NOTE. The conversion of blood pigment into haematoporphyrin involves 

 two processes. Firstly, the acid splits off the protein constituent (globin) and 

 forms acid haematin ; secondly, the acid haematin loses its iron and becomes 

 haematoporphyrin. The first change is effected very readily even by dilute 

 acids, but the separation of the iron from the haematin normally requires 

 highly concentrated mineral acids. It has, however, been shown by Laidlaw 

 that if the blood be first reduced the iron is split off with much greater ease by 

 the acid. An efficient method of reducing defibrinated blood is that of " auto- 

 reduction," in which a tightly corked vessel full of blood is allowed to stand for 

 a few days. If Exercises 307 and 308 be carried out with this reduced blood, 

 care being taken by use of a pipette to prevent re-oxidation, the haemoglobin is 

 entirely converted into haematoporphyrin, no trace of the brown haematin 

 being left. 



It sometimes happens that on pouring the acid solution into water a 

 precipitate is not obtained. In such cases it is necessary to repeat the experi- 

 ment, but to pour the acid haematoporphyrin into a smaller volume of water. 

 On making a portion of this alkaline with 40 per cent, soda the spectrum of 

 alkaline haematoporphyrin can generally be observed. It is sometimes 

 necessary to examine such a solution in a thick layer, as in a beaker. 



309. Preparation of haemin crystals. 



A small drop of blood is spread to form a film on a glass slide 

 and slowly evaporated till it is quite dry. To the film add two drops 

 of a o-i per cent, solution of potassium chloride in glacial acetic 

 acid. Cover with a slip and heat over a very small flame till bubbles 

 appear and the solution is boiling. Immediately allow a drop or two 

 more of the reagent to run under the cover slip and examine under a 

 microscope. 



NOTE. Haemin is the di-acetyl ester of haematin hydrochloride. The 

 above method is an extremely simple one of obtaining good specimens of the 

 crystals, the production of which was formerly used as a test for blood in cloth, 

 etc. It is important not to burn the blood during the drying process, and also 

 to be sure that the acetic solution is rapidly brought to the boiling point. 



The test can be applied to dilute solutions of haemoglobin by acidifying 

 with acetic acid, precipitating with freshly prepared tannic acid, and treating 

 the dried precipitate in a slide as described above. Suspected blood stains on 

 linen, instruments, etc., should be extracted with a little alkali, the solution 

 evaporated to dry ness and treated as above. 



D. Blood constituents and their analysis. 



Glucose. Human blood contains about o-i per cent, 

 of glucose. The available evidence indicates that this 

 exists in a free state in the blood, and that it is equally 



