868 PHYSIOLOGY 



DERIVATIVES OF HAEMOGLOBIN. Haemoglobin is a compound of 

 an iron-containing coloured group (the prosthetic group) with a protein, 

 which probably varies somewhat in different animals. The prosthetic group 

 is identical in every case where it has been examined. A separation of the 

 prosthetic group from the protein moiety can be effected with extreme ease, 

 and occurs whenever the haemoglobin is treated with weak acids, with 

 alkalies, or is heated above 70 C. The protein group is known as globin. 



In order to separate globin, oxyhaemoglobin crystals are dissolved in water and 

 treated with small quantities of very dilute hydrochloric acid. A precipitate of pig- 

 ment forms which, if the haemoglobin used be free from inorganic salt, rapidly dissolves 

 in excess of the acid. Alcohol and ether are then added in such relative quantities 

 that the ether separates rapidly from the aqueous solution. The colouring matter 

 (hsematin) dissolves in the ether, whilst the protein (globin) remains in solution 



in the water. The solutions are separated by a 



+ "^i-^V^t^ separating funnel and ammonia added carefully to 



L/ \ "^ ^ ~ VJr *^ e a( l ueolls solution. This throws down a pre- 



V 4. ^ *% **" * cipitate of the protein, -which is soluble in acids 



sfc S I ^ Y ** ^ V* I an d alkalies and coagulable on heating ; the coagu- 



v , "T -~ v \ r V s "J^ ^ lum however is soluble in acids. It is precipitated 



4/ y ^ Mf.V*\N ^7 ammonia in the presence of ammonium chloride. 

 ^ ,4 ^^- A \~*<- I* contains as much as 16-89 per cent, nitrogen, 

 // and yields a considerable amount of the basic 



^ "^ 1 , derivatives on hydrolysis. It is therefore classified 

 ^C\^ \~\~ with the histones. 



* Haemoglobin yields about 94 per cent, of 



/>*t globin and about 4*5 per cent, of the chromo- 



Fio.373. Hsemhi crystals. g enic group, haematin. In order to obtain 



kcematin in a pure condition, it is usual to 



start with the crystalline derivative of haemoglobin known as hcemin. 

 When some dried blood is heated with a crystal of common salt and 

 placed in acetic acid on a slide, a residue is obtained in which a number 

 of reddish-brown needles are embedded known as Teichmann's crystals or 

 haemin crystals (Fig. 373). The preparation of these crystals is often used 

 as a convenient test for the identification of blood. 



In order to obtain them in large quantities the following method, devised by 

 Chalfejew, is employed. One volume of defibrinated blood is added to four volumes of 

 glacial acetic acid previously heated to 80 C. As soon as the temperature has fallen to 

 60 C. the liquid is again warmed, and then allowed to cool. Crystals are formed 

 which are allowed to stand for twelve hours and are then separated and washed by 

 decantation, first with distilled water and then with graduated strengths of alcohol. 

 In order to purify these crystals, the crude material is shaken for fifteen minutes with a 

 mixture of chloroform and pyridine. The solution is filtered and then thrown into 

 glacial acetic acid previously saturated with sodium chloride and heated to 105 C. 

 A few drops of concentrated hydrochloric acid are then added and the mixture allowed 

 to stand for twenty-four hours. The crystals which separate out are filtered off, 

 washed with dilute acetic acid, and then dried. 



crystals have been regarded as hydrochloride of hseniatin. 

 Elementary analysis shows that they have the following formula (Will- 

 stiitter) : (C 33 H 3 OiN 4 CLFe. By dissolving haemin in alkalies and throwing 



