APPENDIX. 327 



(1.) Albuminoids or Proteids are the most important of the nitroge- 

 nous animal compounds, one or more of them entering as essential parts 

 into the formation of all living tissue. In the lymph, chyle, and blood, 

 they also exist abundantly. Their atomic formula is uncertain. Their 

 composition may be taken as 



Carbon . . from 51 -5 to 54 '5 



Hydrogen . . " 6-9 " 7 '3 



Nitrogen . . " 15 '2 " 17' 



Oxygen . . " 20-9 " 23 -5 



Sulphur . -3 " 2- (Hoppe-Seyler.) 



Physical Properties. Proteids are all amorphous and non-crystalliza- 

 ble, so that they possess as a rule no power (or scarcely any) of passing 

 through animal membranes. They are soluble, but undergo alteration in 

 composition in strong acids and alkalies; some are soluble in water, others 

 in neutral saline solutions, some in dilute acids and alkalies, few in 

 alcohol or ether. Their solutions have a left-handed action on polarized 

 light. 



Chemical Properties. Certain general reactions are given for proteids. 

 They are a little varied in each particular case: 



i. A solution boiled with strong nitric acid, becomes yellow, 



and this yellowness gets darker on addition of ammonia 



(xantho-proteic reaction), 

 ii. With potassium ferrocyanide and acetic acid, they give a white 



precipitate, 

 iii. With a trace of copper sulphate and an excess of potassium 



or sodium hydrate they give a purple coloration, 

 iv. With Millon's reagent (mixed nitrate and nitrite of mercury?), 



they give a white or pinkish precipitate, becoming more 



pink on boiling. 

 v. When boiled with sodium sulphate and acetic acid, a white 



precipitate is thrown down. 



It is usual to place Proteids into the following sub-classes, thus: 



I. II. III. 



NATIVE ALBUMINS. DEBITED ALBUMINS. GLOBULIN. 

 Egg- Albumin. Acid- Albumin. (a.) Globulin. 



Serum-Albumin. Alkali- Albumin. (b.) Myosin. 



Casein. (c. ) Fibrinoplastic Globulin, 



(d.) Fibrinogen. 

 (e.) Vitellin, etc. 



IV. FIBRIN. V. -PEPTONES. VI. COAGULATED PKOTEIDS. 

 VII. LARDACEIN. 



CLASSES OF PROTEIDS. 



I. The Native Albumins are soluble in water and in saline solutions 

 coagulable by heating, not precipitated by acetic or normal phosphoric 

 acid. Serum-albumin (p. 85, Vol. I.) is distinguished from egg-albumin 



