THE CHEMICAL COMPOSITION OF THE BODY. [CH. xxv. 



differ in their solubilities. This difference in solubility may be 

 stated in tabular form as follows : 



TTT -r. (These products of digestion will be 



Class III. Proteoses ' ,. l , .. 



TTT _ 4 studied in connection with that 



Class IV. Peptones 



( subject. 



Class V. Coagulated Proteids. -- There are two sub- 

 divisions of these : 



(a) Proteids in which coagulation has been produced by heat ; 

 they are insoluble in water, saline solutions, weak acids, and weak 

 alkalis ; they are soluble after prolonged boiling in concentrated 

 mineral acids; dissolved by gastric and pancreatic juices, they 

 give rise to peptones. 



(b) Proteids in which coagulation has been produced by 

 ferments : i. Fibrin (see BLOOD). ii. Myosin (see MUSCLE). 

 iii. Casein (see MILK). 



Appendix to the class of simple proteids. Albuminates 

 are compounds of proteid with mineral substances. Thus, if a 

 solution of copper sulphate is added to a solution of albumin 

 a precipitate of copper albuminate is obtained. Similarly, by 

 the addition of other salts of the heavy metals other metallic 

 albuminates are obtainable. 



The albuminates which are obtained by the action of dilute 

 acids and alkalis on either albumins or globulins are, however, of 

 greater physiological interest, and it is to these we shall confine 

 our attention. The general properties of the acid-albumin or 

 syntonin, and the alkali-albumin, which are thereby respectively 

 formed, are as follows : they are insoluble in pure water, but 

 are soluble in either acid or alkali, and are precipitated by 

 neutralisation unless certain salts like sodium phosphate are 

 present. Like globulins, they are precipitated by saturation with 

 such neutral salts as sodium chloride and magnesium sulphate. 

 They are not coagulated by heat. 



A variety of alkali-albumin (probably a compound containing a 



