CHEMIC COMPOSITION OF THE HUMAN BODY. 33 



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 neu- 

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

 After the precipitate is washed, it is found to be insoluble 

 in distilled water and in neutral saline solutions. In acid 

 solutions it is not coagulated by heat. 



(b) 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 saline solutions; it is not 

 coagulable by heat. 



(c) Caseinogen. This is the principal proteid of milk, in which 



it exists in association with an alkali, and hence was formerly 

 regarded as a native alkali-albumin. It is precipitated by 

 acetic acid and by magnesium sulphate. It is coagulated by 

 rennet that is, separated into an insoluble proteid, casein or 

 tyrein, and a soluble albumin. Calcium phosphate seems to 

 be the natural alkali necessary to this process, for if it be 

 removed by dialysis, or precipitated by the addition of 

 potassium oxalate, coagulation does not take place. 



4. COAGULATED PROTEIDS. . 



Although these proteids are not found as constituents of the 

 animal organism, they possess much interest on account of their 

 3 



