CHEMICAL COMPOSITION. xxxv 



deprived of iron, the haematin retains its colour, and has suffered no appreciable 

 change in character. It would seem therefore that iron, although a constant ingre- 

 dient in the red corpuscle, is not an essential constituent of haematin, and it is, at 

 any rate, clear that the red colour of the blood is not caused by iron. 



Globulin. When the haematin has been extracted from the blood- 

 corpuscles by the foregoing method, the globulin and envelopes remain in 

 combination or mixture with sulphuric acid. Globulin is a protein com- 

 pound, agreeing very nearly with albumen and casein in elementary com- 

 position, so far as this has been ascertained, but most resembling the latter 

 substance in its general characters. Globulin is nearly insoluble in pure 

 water, but readily dissolves on a very slight addition of either an alkali or 

 an acid. Weak acids throw it down from its solution in alkali, but when 

 added in slight excess re-dissolve it. In like manner it is precipitated by 

 alkalies from its solutions in acids and re-dissolved by excess. From neither 

 of these solutions is it thrown down by heat. It is dissolved by neutral salts, 

 and from this solution heat throws it down in an insoluble precipitate. 

 From its slightly alkaline solution in water it is thrown down by a stream 

 of carbonic acid, and may be re-dissolved by passing air or oxygen through 

 the liquid. Its precipitate is distinguished from that of other albuminoids 

 by beiug always in form of fine granules or molecules. But the most im- 

 portant and distinctive character of globulin is its fibrino-plastic property, 

 to be afterwards further referred to, by which it co-operates with another 

 protein -substance in producing solid fibrin ; this property is destroyed by 

 exposure of the solution to a boiling heat. 



Globulin forms the greater part of the crystalline lens, and it is no doubt present 

 in the pale blood-corpuscles ; it exists also in the chyle and lymph, the cornea, the 

 aqueous humour, and various other tissues and fluids, if its presence is to be inferred 

 from the manifestation of the fibrino-plastic property. The globulin of the red cor- 

 puscles is crystallisable, as will be presently explained. 



The cruor, or the soluble matter of the red corpuscles, which consists of 

 the globulin and colouring principle (the cruorin of Stokes) together, forms 

 in water a solution (maintained probably by soda and salts) which in its 

 effects with re-agents agrees with solution of globulin. Berzelius reckons 

 the relative proportions of globulin and hseinatin as 94 '5 of the former, and 

 5- 5 of the latter. Schmidt makes them 87 '59, and 12-41 respectively. The 

 corpuscles also contain a solid phosphuretted fat in small quantity, which 

 may be stated at rather more than 2 parts in the 100 of dried corpuscles. 

 100 parts of dried cruor yield by calcination about 1'3 of brown alkaline 

 ashes, which consist of carbonate of alkali with traces of phosphate 0'3, 

 phosphate of lime 0*1, lime 0'2, subphosphate of iron O'l, peroxide of iron 

 0*5, carbonic acid and loss O'l. 



Blood-crystals. In the blood of man and various animals, when drawn 

 from the vessels and set aside for a time, red crystals occasionally appear, 

 consisting of globulin tinted by the colouring matter : and their formation 

 may be promoted by adding water to defibriuated blood so as to set free the 

 cruor from the corpuscles, and exposing the watered blood first to a stream 

 of oxygen and then to carbonic acid. Or a drop of blood, defibrinated or 

 not, is to be mixed with a little water on a slip of glass, exposed for a little 

 to the air, then breathed upon, and finally covered with thin glass and 

 placed in a bright light, which seems to favour the crystallisation. The 



