74:0 APPENDIX. 



It is insoluble in dilute acids and in gastric juice at the temperature 

 of the body. It is colored brown by iodine and bluish-purple by methyl 

 violet. 



(2.) Tlie Gelatins or Nitrogenous Bodies other than Proteids. 



(A) Gelatin. Gelatin is contained in bone, teeth, fibrous connective 

 tissues, tendons, ligaments, etc. It may be obtained by prolonged action 

 of boiling water in a Papin's digester, or of dilute acetic acid at a low 

 temperature (15 C.). 



Properties. The percentage composition is 0, 23.21, H, 7.15, N, 

 18.32, 0, 50.76, S, 0.56. It contains more nitrogen and less carbon than 

 proteids. It is amorphous, and transparent when dried. It does not 

 dialyze; it is insoluble in cold water, but swells up to about six times 

 its volume: it dissolves readily on the addition of very dilute acids or 

 alkalies. It is soluble in hot water, and forms a jelly on cooling, even 

 when only 1 per cent of gelatin is present. Prolonged boiling in 

 dilute acids, or in water alone, destroys this power of forming a jelly on 

 cooling. 



A fairly strong solution of gelatin 2 per cent to 4 per cent gives 

 the following reactions: 



(A) With proteid tests: (i.) Xanthoproteic test. A yellow color with 

 no previous precipitate with nitric acid, becoming darker on the 

 addition of ammonia, (ii.) Biuret test. A violet color, (iii.) 

 Millon's test. A pink precipitate, (iv.) Potassium ferrocyanide 

 and acetic acid. No reaction, (v.) Boiling with sodium sul- 

 phate and acetic acid. No reaction. 



(B) Special reactions: (i.) No precipitate with acetic acid, (ii.) No 

 precipitate with hydrochloric acid, (iii.) A white precipitate 

 with tannic acid, not soluble in excess or in dilute acetic acid. 

 (iv.) A white precipitate with mercuric chloride, unaltered by 

 excess of the reagent, (v.) A white precipitate with alcohol, 

 (vi.) A yellowish-white precipitate with picric acid, dissolved on 

 heating and reappearing on cooling. 



Bone consists of an organized matrix of connective tissue which yields 

 gelatin and inorganic salts. 



Inorganic salts can be removed by digesting it in hydrochloric acid. 

 The gelatinous matter left retains the form of the bone. By long boiling 

 in water it is converted into a solution of a gelatin. 



When bone is heated, the first action is to decompose the organic 

 matter, leaving a deposit of carbon. On further ignition in air this car- 

 bon burns away, and only inorganic salts (principally calcic phosphate) 

 are left. 



(B) Mucin. Mucin is the characteristic component of mucus; it is 

 contained in foetal connective tissue, tendons, and salivary glands. It 



