THE PEOTEIDS 



27 



Class III. Proteoses ] These products of digestion will be studied 



Class IV. Peptones J in Lessons VI. and VII. 



Class V. Coagulated Proteids. — There are two principal subdivi- 

 sions of these : — 



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

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

 alkalis ; 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 fer- 

 ments : — 



i. Fibrin (see Blood), ii. Myosin (see Muscle), iii. Casein (see 

 Milk). 



Directions for testing for and separating proteids will be found at 

 the end of this elementary course. 



Albuminates 



Albuminates are compounds of proteid (albumin or globulin) vdth 

 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 of considerable 

 physiological interest because they are formed during digestion, and 

 it is to these we shall chiefly confine our attention. The general 

 properties of the acid-alhiimin, or syntonin, and the alkali-allnmiin 

 which are thereby respectively formed will be gathered from the 

 practical exercise which stands at the head of this lesson. They are 

 insoluble in pure water, but are soluble in either acid or alkali, and 

 are precipitated by neutralisation unless disturbing influences Hke the 

 presence of sodium phosphate are present. It may also be added 

 that, like globulins, they are precipitated by saturation with such 



