CHEMICAL COMPOSITION OP THE BODY. 85 



of the body, but may be obtained by boiling connective tissue, articular 

 fibro-cartilage, or bone, with water. The solution gelatinizes on cooling, 

 even when the gelatin is only present in the proportion of 1 per cent. It is 

 precipitated by alcohol and ether, but not by acids, with the exception of 

 tannic acid, which constitutes its most delicate test. It is also precipitated 

 by chlorine water and corrosive sublimate, but not by other salts of mer- 

 cury, nor by those of silver, copper, lead, or alum, nor by potassium ferro 

 or ferricyanide. Its percentage constitution when procured from tendon is 

 C 50.9, H 7.2, N 18.3, O .23, and S .56. When acted on by oxidizing 

 agents, it furnishes the same products of disintegration as the albuminated 

 compounds, and with sulphuric acids and alkalies, it yields Leucin and 

 Glycin. 



ELASTIN is the basis of elastic tissue, and may be obtained from it by 

 boiling it successively with alcohol, ether, water, concentrated acetic acid, 

 diluted alkaline lye, and hydrochloric acid. When the residue is thoroughly 

 washed it forms a yellowish fibrous mass still possessing great elasticity, 

 which dissolves only in concentrated alkalies. When heated on platinum, 

 it burns away without leaving any residue. It differs from albumen in 

 being destitute of sulphur. The composition of a portion taken from the 

 ligamentum nuehse, as given by W. Miiller, is C 55.72, H 7.67, N 15.71, 

 O 20.7. 



CHONDRIN is obtained by boiling cartilage or the cornea of the eye with 

 water, and appears to be a modification of gelatin, from which it differs in 

 being precipitated by acetic acid, diluted mineral acids, and the salts of 

 alum, iron, lead, silver, and copper; whilst its solutions are only rendered 

 slightly turbid by tanuic acid. When boiled with sulphuric acid it yields 

 no glycin, but only leuciu. It is not as yet accurately ascertained whether 

 gelatin and chondrin pre-exist in the tissues from which they are obtained, 

 or are produced in the act of boiling, for on the one hand they cannot be 

 obtained by maceration in cold water, whilst on the other the action of 

 tannic acid on the tissues seems to be of the same nature as on the solu- 

 tion; and when exerted upon the connective tissues of the skin, effects its 

 conversion into leather. Its percentage composition is C 49.9, H 6.6, 

 28.6, S 0.4. 



KERATIN constitutes the basis of the various horny tissues, as epithelium, 

 epidermis, nails, hoofs, claws, horn, wool, hair, and feathers. It is char- 

 acterized by swelling and becoming soft in boiling water, though it neither 

 dissolves in this fluid, unless the temperature is much raised by pressure, 

 nor in ether or alcohol. With the exception of hair the tissues in which it 

 is contained are soluble in acetic acid and in alkalies. It is colored yellow 

 by nitric acid, and under the action of sulphuric acid develops much leucin 

 and tyrosin. The horny tissues in their early state are all composed of soft 

 cells, which subsequently become modified in form, and much firmer in con- 

 sistence. They contain C, H, N, O, and S in proportions that, whilst closely 

 similar to those of the albuminous compounds from which they are derived, 

 have not yet been accurately determined. 



MUCIN. A substance possessing in a high degree the power of absorbing 

 water, and swelling up to a gelatinous and sticky mass of semifluid consis- 

 tence. No precipitate or coagulation occurs in mucin at a boiling heat, nor 

 is any produced by acetic acid, the mineral acids, or potassium ferrocyanide. 

 It occurs in the body in the mucous fluids, and may be obtained by boiling 

 water from the fetal connective tissue. It is contained in the fluid of Ranula. 

 It differs from albumen in being free from sulphur, and in containing a 

 smaller amount of carbon and nitrogen. 



PYIN presents features closely analogous to those of mucin, except that 



