VEGETABLE PROTEIDS. 459 



gelatinous and again fluid when heated. The syntonin from muscle is an acid- 

 albuminate. It is converted into myosin by milk of lime and ammonium chlorid. 



The second group comprises the complex albuminous bodies. These are pro- 

 teins combined with bodies of complex composition and they are also designated 

 proteids. They are precipitated by alcohol, which coagulates them after long- 

 continued action. Heat does not cause coagulation. They are generally pre- 

 cipitated from their solutions by slight acidulation. They are readily soluble in 

 dilute alkalies. The second group comprises: 



Chromoproteids, that is combinations of protein with pigment. These in- 

 clude : 



Hemoglobin, whose combinations and derivatives are described on pp. 55-63. 



Glycoproteids, that is combinations of protein with carbohydrates. These 

 include : 



Mucin, probably present in various slightly different modifications. It is 

 richer in oxygen, but poorer in nitrogen and carbon, than albumin, free from 

 phosphorus, and contains up to 1.79 per cent, of sulphur and up to 13.5 per 

 cent, of nitrogen. It is liquefied in water into a ropy mucous mass, but it is 

 insoluble in water. On addition of alkali it is converted into a neutral ropy 

 solution. It serves as a protecting substance against the entrance of injurious 

 agents. It is precipitated by a small amount of acetic acid and is redissolved by 

 a larger amount of the same acid. It is precipitated also by alcohol, the resulting 

 precipitate being soluble in water. Acetic acid and potassium ferrocyanid cause no 

 precipitation, although nitric acid and other mineral acids do. Mucin yields all 

 the color-reactions of the albuminous bodies. It is present in saliva, bile, the 

 mucous glands, the secretions from mucous membranes, in "mucous" tissue 

 and in the tendons. In addition it is occasionally found pathologically in 

 cysts (in the lower animals, especially in snails and in the skin of holothurians) . 

 On boiling with water or on standing in alcohol it is transformed into coagulated 

 albumin. Alkalies and lime-water transform it into alkali-albuminate, acids into 

 acid-albuminate. On decomposition it yields leucin and 7 per cent, of tyrosin. 

 The mucins react like glucosids. At high temperatures they break up under the 

 influence of dilute mineral acids into a proteid and a carbohydrate, namely, animal 

 gum. 



Peptone and propeptone are discussed on p. 298; their demonstration in the 

 urine on p. 496. Peptone is found also in dry lupins, in oats, etc., and less in 

 germinating seed. There may yet be mentioned proteic acid, precipitated from 

 the meat-juice of animals (fish) by Limpricht with the aid of acids; and 

 finally amyloid, encountered partly in the form of laminated granules on the brain 

 and in the prostate gland, partly (pathologically) as a glistening infiltration of the 

 liver, spleen, kidneys, coats of the vessels, and recognizable from the blue dis- 

 coloration on addition of iodin and sulphuric acid (like cellulose), and the red 

 discoloration on adding iodin. It can with difficulty be converted into albuminate 

 by alkalies and acids. 



APPENDIX: VEGETABLE PROTEIDS. 



Plants contain, although in distinctly smaller amount than animals, proteids 

 of various kinds. These occur either in liquid (swollen) form, particularly in the 

 juices of living plants, or in solid form. They resemble the animal albuminates 

 in composition and reaction. There are distinguished: 



I. The vegetable albumins. 



II. The vegetable globulins. Of the globulins forming crystals or spheroids 

 that were formerly grouped together under the names conglutin and vitellin, 

 together with legumin, the following may be mentioned: Edestin in grain, amandin 

 in almonds, corylin in nuts, excelsin in the Para nut, avenalin in oats, conglutin 

 in lupins. The globulins include as a decomposition-product glutin, an important 

 constituent of wheat, whose glutinous property makes it possible to convert a 

 mixture of flour and water into a coherent dough. Gluten can be obtained from 

 wheat-flour, which may contain as much as 17 per cent., by washing the dough 

 repeatedly with water. Thus prepared, it is viscid, gray, insoluble in water and 

 alcohol, soluble in dilute acids (for example i in 1000 parts of hydrochloric acid) 

 and in alkalies. Gluten results from a myosin-like globulin-substance, which is 

 transformed by a ferment in the presence of water into gluten. 



III. The nucleins, which comprise a special group of readily decomposed 

 complex proteids, containing phosphoric acid in firm combination. They form the 

 chromatin-substance of the cell-nucleus (whence the name) , as well as the tingible 



