10 THE HUMAN BODY. 



is very like egg-albumin in its properties. It is coagulated 

 (like the white of an egg) when boiled, arid then passes into 

 the state of coagulated proteid which is, unlike the original 

 serum-albumin, insoluble in dilute acids or alkalies or in 

 water containing neutral salts in solution. All other proteids 

 can by appropriate treatment be turned into coagulated 

 proteid. 



Fill-in. This forms in blood when it " clots," either in- 

 side or outside of the Body; it is insoluble in water and dilute 

 acids or alkalies; soluble in strong acids and alkalies and, 

 though slowly, in ten per cent neutral saline solutions. 



Myosin. This is derived from the muscles, in which it 

 develops and solidifies after death, causing the "death-stiffen- 

 ing." 



Globulin exists in the red globules of the blood and dis- 

 solved in some other liquids of the body. In the blood-cor- 

 puscles it is combined with a colored non-proteid substance 

 to form licemoglolin, which is crystallizable. Allied sub- 

 stances, paraglolulin and fibrinogen, are found dissolved in 

 the blood-liquid. When blood clots the fibrinogen gives rise 

 to fibrin. 



Casein or, as it is better named, caseinogen exists in 

 milk. Its solutions do not coagulate spontaneously or, like 

 that of serum-albumin, on boiling. When milk turns sour on 

 keeping, or when it is very slightly acidulated with dilute 

 acetic acid, the casein is precipitated. The clot or curd which 

 forms when milk is gently warmed with gastric juice or with 

 rennet, is also derived from caseinogen; it differs from true 

 casein and is named tyrein : it is the chief constituent of 

 cheese. 



Peptones. These are formed in the alimentary canal by 

 the action of some of the digestive liquids upon the proteids 

 swallowed as food. They contain the same elements as the 

 proteids and give the xantho-proteic and Millon's reactions, 

 but are not precipitated by boiling with acetic acid and 

 sodium sulphate. Their great distinctive character is, how- 

 ever, their diffusibility. The proteids proper will not dialyze 

 (see Physics), but the peptones in solution pass readily 

 through moist animal membranes. 



Albuminoids or Gelatinoids. These contain carbon, 

 hydrogen, oxygen and nitrogen, but rarely any sulphur. Like 

 the proteids, the nearest chemical allies of which they seem 



