COLOURING xMATTERS. 39 



a considerable turbidity, and ultimately causes a slight white 

 precipitate. The nature of this precipitate remains doubtful. 

 The spirit-extract is thrown down from its solution by infusion 

 of galls and basic and neutral acetates of lead, but not by 

 bichloride of mercury. 



The alcohol-extract of milk is obtained by the evapora- 

 tion of the yellow anhydrous alcoholic solution that has been 

 already referred to. It exists in very minute quantity, is of a 

 yellow colour, and is not materially affected by infusion of galls, 

 basic or neutral acetates of lead, or bichloride of mercury. 



Ptyalin and pyin may be regarded as water-extracts of saliva 

 and pus. 



10. Colouring Matters. 



1. THE BLOOD. 



a. Hamatin. This colouring matter is inclosed in thin sacs 

 or vesicles, composed of a protein-compound, globulin : these 

 vesicles exist in countless numbers in the circulating fluid, and 

 are termed blood-corpuscles. 



It has been generally assumed that this pigment exists in two 

 distinct chemical states in arterial and venous blood, ha\iug in 

 the former an excess of oxygen, in the latter an excess of carbon 

 or carbonic acid. Mulder has, however, shown that its ele- 

 mentary composition is the same, whether obtained from arterial 

 or from venous blood, and that it may be represented by the 

 formula! C^^ H,^„ Ng O^ Fe. Its composition seems likewise to 

 be identical in all vertebrated animals.- 



Various methods have been proposed for the exhibition of 

 pure hsematin. The following, adopted by Simon, is perhaps 

 the simplest. AMiipt and thoroughly dried blood must be 

 pulverized, and its fat removed by repeated extraction with 

 ether. It must then be boiled with anhvdi'ous alcohol, and 

 during the process of ebullition a quantity of sulphuric acid, di- 

 luted with cold alcohol, must be added, sufficient to communicate 



' See Appendix I, Note 16. 



^ Lecanu examined hsematin from human blood, and from that of the ox, domestic 

 hen, duck, frog, carp, and mackerel. The only difference was in the proportion of 

 peroxide of u'on left when the hreniatin was incinerated. 



