PROTEIDS 81 



Histons ; contain 35 to 42 per cent of their nitrogen as basi * nitrogen. 



Protamins; contain 63 to 88 per cent of their nitrogen as basic nitro- 

 gen. 

 Compound Proteids. 



Hemoglobin; decomposes into a proteid and a chromogen. 



Nucleoproteid; decomposes into a proteid and nucleic acid. 



Glycoproteid ; decomposes into a proteid and a reducing substance, 



mucin. 



Albuminoid substances; mucin, keratin, albumoid, collagen, elastin, 

 etc. 



The Albumins. Of native albumins there are several varieties: 

 egg albumin; serum albumin; lact albumin, etc. 



When in solution in water it is a transparent, frothy, yellowish fluid, 

 neutral or slightly alkaline in reaction. It gives all of the general proteid 

 reactions. On digestion it yields 8 per cent of argenin, 22.6 per cent of 

 leucin, and 2 per cent of tyrosin. 



At a temperature not exceeding 40 C. it is dried up into a yellowish, 

 transparent, glassy mass, soluble in water. At a temperature of 70 C. it is 

 coagulated into a new substance, coagulated proteid, which is quite insoluble 

 in water. It is coagulated also by the prolonged action of alcohol; by strong 

 mineral acids, especially by nitric acid; also by tannic acid, or carbolic acid; 

 and by ethers. The coagulum is soluble in caustic soda. 



With strong nitric acid the albumin is precipitated at the point of contact 

 with the acid in the form of a fine white or yellow ring. 



Serum Albumin is contained in blood serum, lymph, serous and synovial 

 fluids, and in the tissues generally; it may be prepared from serum after 

 removal of paraglobulin, by a saturation with sodium sulphate. It appears 

 in the urine in the pathological condition known as albuminuria. 



It gives similar reactions to egg albumin, but differs from it in not being 

 coagulated by ether. It also differs from egg albumin in not being easily 

 precipitated by hydrochloric acid, and in the precipitate being easily soluble 

 in excess of that acid. Serum albumin, either in the coagulated or precipi- 

 tated form, is more soluble in excess of strong acid than egg albumin. 



Globulins. Globulins are found in egg; in blood, lymph, and 

 other body fluids; and in most protoplasm. 



The globulins give the general proteid tests; are insoluble in water; are 

 soluble in dilute saline solutions; are soluble in acids and alkalies forming 

 the corresponding derived albumin. 



Most of them are precipitated from their solutions by saturation with 

 solid sodium chloride, magnesium sulphate, or other neutral salt. They 

 are coagulated, but at different temperatures, on heating. 



A globulin is obtained from the crystalline lens by rubbing it up with 

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