20 



22. Metallic albuminates. Add to separate tubes of albumin 

 solution, a crystal each of copper sulphate, silver nitrate and 

 a small amount of mercuric chloride. In each of the three 

 tubes metallic albuminates will be precipitated. 



23. Coagulated- proteids are obtained by the action of heat, 

 enzymes, acids, and other reag-ents on native proteids, by a 

 process of unknown nature, and have been found in the liver 

 and other glands. Fibrin is a coagulated proteid formed by 

 the action of the fibrin ferment on the fibrinogen of blood 

 plasma. 



24. Proteoses or Albumoses. Proteoses are the products of 

 the hydrolysis of proteids. They are important intermediate 

 products in the digestion of proteids in the animal body, are 

 soluble in water, not coagulated by heat, and are precipitated 

 by saturating their solution with ammonium sulphate. 



25. Compound proteids on hydrolysis yield as products of 

 the first splitting a simple proteid and some non-proteid sub- 

 stances. They are subdivided, according to this non-proteid 

 result, as hemoglobins, glycoproteids, and nucleoproteids. 



26. Hemoglobins on hydrolysis yield a simple proteid and 

 hematin. Hemoglobin is the coloring agent of the blood and 

 enters into combination with certain gases — for instance, car- 

 bon dioxide, nitrogen dioxide, and hydrocyanic acid — more 

 readily than with oxygen, and the poisonous properties of 

 these gases are due largely to their power of satisfying the 

 affinities of the hemoglobin, and in this way rendering it in- 

 capable of taking up oxygen. 



Hemoglobin is soluble in water, in dilute solutions of 

 albumin, of the alkalies and their carbonates, and in sodium 

 or ammonium phosphate. It is insoluble in strong alcohol, 

 ether, and in the volatile and fatty oils. With the spectro- 

 scope both oxyhemoglobin and reduced hemoglobin show char- 

 acteristic absorption bands. Hemoglobin crystals may be 

 obtained, which differ in shape and solubility in water accord- 

 ing to the species of animal from which the blood is obtained. 



27. Glycoproteids yield a substance capable of reducing 

 an alkaline solution of cupric oxide. They are divided into 

 mucins, mucoids, and chondroproteids. 



Mucins are secreted by mucous glands and certain mucous 

 membranes. Mucin also occurs in connective tissue and in the 



