88 HANDBOOK OF PHYSIOLOGY. 



On shaking the reduced haematin with air or oxygen the two bands are 

 replaced by the single band of alkaline haematin. 



Haematoidin. This substance is found in the form of yellowish 

 crystals in old blood extravasations, and is derived from the haemoglobin. 

 Their crystalline form and the reaction they give with nitric acid seem 

 to show them to be identical with BiliruUn, the chief coloring matter 

 of the Bile. 



Haemin. One of the most important derivatives of haematin is has- 

 min. It is usually called Hydrochlornte of Hcematin (or hydrochloride), 

 but its exact chemical composition is uncertain. Its formula is C 68 , H 70 , 

 N 8 , Fe 2 , 10 , 2 HC1, and it contains 5.18 per cent of chlorine, but by 

 some it is looked upon as simply crystallized haematin. Although diffi- 

 cult to obtain in bulk, a specimen may be easily made for the microscope 

 in the following way : A small drop of dried blood is finely powdered 

 with a few crystals of common salt on a glass slide, and spread out ; a 

 cover glass is then placed upon it, and glacial acetic acid added by means 

 of a capillary pipette. The blood at once turns of a brownish color. 

 The slide is then heated, and the acid mixture evaporated to dryness at 

 a high temperature. The excess of salt is washed away with water from 

 the dried residue, and the specimen may then be mounted. A large 

 number of small, dark, reddish black crystals of a rhombic shape, some- 

 times arranged in bundles, will be seen if the slide be subjected to micro- 

 scopic examination. 



The formation of these haemin crystals is of great interest and impor- 

 tance from a medico-legal point of view, as it constitutes the most certain 

 and delicate test we have for the presence of blood (not of necessity the 

 blood of man) in a stain on clothes, etc. It exceeds in delicacy even the 

 spectroscopic test. Compounds similar in composition to haemin, but 

 containing hydrobromicand hydriodic acids, instead of hydrochloric, may 

 be also readily obtained. 



Estimation of Haemoglobin. The most exact method is by the 

 estimation of the amount of iron in a given specimen of blood, but as 

 this is a somewhat complicated process, a method has been proposed 

 which, though not so exact, has the advantage of simplicity. This con- 

 sists in comparing the color of a given small amount of diluted blood 

 with glycerin jelly tinted with carmine and picrocarmine to represent a 

 standard solution of blood diluted one hundred times. The amount of 

 dilution which the given blood requires will thus approximately repn- 

 sent the quantity of haemoglobin it contains. (Gowers. ) 



Distribution of Haemoglobin. Haemoglobin occurs not only in the 

 red blood-cells of all Vertebrata (except one fis'h [leptocephalus] whose 

 blood cells are all colorless), but also in similar cells in many Worms ; 

 moreover, it is found diffused in the vascular fluid of some other worms 

 and certain Crustacea ; it also occurs in all the striated muscles of Mam- 

 mals and Birds. It is generally absent from unstriated muscle except 

 that of the rectum. It has also been found in Mollusca in certain rnus- 



