PROXIMATE CONSTITUENTS OF THE BODY. 73 



chyle and lymph, and in the serous fluids. But it is in the muscular 

 tissue that so enormous a quantity of a peculiar kind of fibrin is 

 found, which is named fibrin of muscle, or syntonin, from ffuvreivw, 

 sunteino, I contract. Like albumen, fibrin is precipitated, and then 

 hardened, by alcohol: it is precipitated by mineral acids and most 

 metallic salts ; but is redissolved by dilute acids in excess. Blood- 

 fibrin is soluble in a solution of nitre, but syntonin, or muscle-fibrin, is 

 not. In the living body, as we shall hereafter find, both albumen and 

 fibrin exist, sometimes in the solid and sometimes in the liquid state. 



G-elatin is the substance of jellies, size, and glue. It is not proved 

 to exist as gelatin in the living or dead body ; but it is obtained as a 

 product rather than as an educt, by boiling in water any part which 

 contains white connective tissue, such as the areolar tissue, tendons, 

 ligaments, the skin, and the areolar basis of the membranes generally. 

 It is also obtainable from the animal matter of bones by long-con- 

 tinued boiling under pressure, as in a Papin's digester. From carti- 

 lages of a pure kind, a peculiar variety of gelatin, called chondrin, 

 is extracted by boiling m water. No gelatin can be obtained by boil- 

 ing blood, chyle, bile, gastric juice, saliva, milk, brain-substance, or 

 muscle, except in the latter case, such as is derived from areolar 

 tissue. Gelatin and chondrin do not coagulate. Gelatin, as its name 

 implies, gelatinizes on cooling, and is liquefied or dissolved again by 

 heat. One part of gelatin will gelatinize a hundred parts of water. 

 Chondrin is also said to gelatinize, but this is doubtful. Neither gel- 

 atin nor chondrin is precipitated by the red or yellow prussiates of 

 potash, by which they are distinguished from albuminoid bodies. They 

 are, however, precipitated by alcohol, ether, corrosive sublimate, and 

 by tannic acid or tannin, which is the active substance in converting 

 any gelatin-yielding tissue, such, especially, as the skin, into the 

 firm insoluble substance which we call leather. Chondrin is distin- 

 guished from gelatin, by being precipitated by acetate of lead, alum, 

 acids, and a few salts, which do not throw down gelatin. 



Keratin, or horny matter, exists in the hair, nails, and epidermis or 

 cuticle, and also in the denser epithelia. Mucin exists in mucus, 

 which is almost always acid. 



Hcematin, from !/*, haima, blood, is a red coloring matter, which 

 is extracted from the red blood-corpuscles, with the globulin of which 

 it is most intimately united. The compound formed by these two sub- 

 stances, named hcemato- globulin, has a great tendency to crystallize, 

 even in blood simply set aside, but still more so in blood subjected to 

 the successive action of oxygen and carbonic acid. The crystals from 

 human blood are either prismatic or rhombic; from animals, tetrahe- 

 dral, rhombohedral, and hexagonal crystals have been obtained. 

 They are doubly refractive, soluble in acetic acid, ammonia, and water, 

 and even deliquescent ; but they are insoluble in alcohol. In blood 

 extravasated within the body, there are frequently found flat, rhombic 

 crystals, insoluble in water, acetic acid, alcohol, or ether, but soluble 

 in chloroform. These are named hcematoidini, the reactions of which 

 with sulphuric acid resemble those of the bile pigments with nitric 

 acid. Other crystals, named hsematin and hsemin, have also been 



