20 HUMAN PHYSIOLOGY. 



soluble in water, soluble in dilute acids and alkalies, and co- 

 agulating at 75 C. 



(b) Fibrinogen. This proteid is found in blood plasma in asso- 

 ciation with serum-globulin and serum-albumin. It is also 

 present in lymph-tissue fluids and in pathologic transudates. 

 It can be obtained from blood-plasma which has been pre- 

 viously treated with magnesium sulphate on the addition of a 

 saturated solution of sodium chlorid. It is soluble in dilute 

 acids and alkalies, and coagulates at 56 C. 



(c) Myosinogen. This proteid is a constituent of the protoplasm 

 of the muscle-fibers. During the living condition it is liquid, 

 but after death it readily undergoes decomposition into an 

 insoluble portion known as myosin and a soluble albumin. It 

 is soluble in dilute hydrochloric acid and dilute alkalies. It 

 coagulates at 56 C. 



(d) Globin. This is a product of the spontaneous decomposition 

 of the coloring matter of the blood, hemoglobin, and arises 

 when the latter is exposed to the air. 



(e) Crystallin or Globulin. This is obtained by passing a 

 stream of CO 2 through a watery extract of the crystalline lens. 



3. DERIVED ALBUMINS OR ALBUMINATES. 



The proteids of this group are derived from both native albumins 

 and globulins by the gradual action of dilute acids and alkalies, and 

 may be regarded as compounds of a proteid with an acid or an alkali. 



(a) Acid-albumin. This is formed when a native albumin is 

 digested with dilute hydrochloric acid (0.2 per cent.) or dilute 

 sulphuric acid for some minutes. It is precipitated by neutral- 

 ization with sodium hydroxid (o.i per cent, solution). After 

 the precipitate is washed, it is found to be insoluble in dis- 

 tilled water and in neutral saline solutions. In acid solutions 

 it is not coagulated by heat. 



(&) Alkali-albumin. This is formed when a native albumin is 

 treated with a dilute alkali e. g., o.i per cent, of sodium 

 hydroxid for five or ten minutes. On careful neutralization 

 with dilute hydrochloric acid, it is precipitated. It is also 

 insoluble in distilled water and in alkaline solutions ; it is not 

 coagulable by heat. 



