S8 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



The formation of peptones is a process of hydrolysis ; peptones 

 may be formed by other hydrating agencies hke superheated steam 

 and heating with dilute mineral acids. There are certain inter- 

 mediate steps in this process ; the intermediate substances are called 

 propeptones or proteoses. The word ' proteose ' is the best to em- 

 ploy : it includes the albumoses (from albumin), globuloses (from 

 globulin), vitelloses (from vitellin), &c. Similar substances are also 

 formed from gelatin (gelatoses) and elastin (elastoses). 



Another intermediate step in gastric digestion is called para- 

 peptone : this is acid-albumin or syntonin. In classifying the pro- 

 ducts of digestion it will be convenient to take albumin as our 

 example, but we must remember that globulin, myosin, and all the 

 other proteids form corresponding products. The products of 

 •digestion may be classified according to the order in which they are 

 formed as follows : — 



1. Parapeptone or acid-albumin. 



/, ^ -P, , ,, ) The primary albumoses, i.e. 



(a) JProto-albumose , ... <. ^ 



o -r> i /'i.\ XT 4. iu r those which are formed 



2. Propeptone -j (o) Hetero-albumose 



•3. Peptone. 



(c) Deutero-albumose 



It is very doubtful whether all the albumin passes through the 

 acid-albumin stage. 



Peptones.— These are the final products of the action of gastric 

 juice on native proteids. 



They are soluble in water, are not coagulated by heat, and are 

 not precipitated by nitric acid, copper sulphate, ammonium sulphate, 

 and a number of other precipitants of proteids. They are precipi- 

 tated but not coagulated by alcohol. They are also precipitated by 

 tannin, picric acid, potassio-mercuric iodide, phospho-molybdic acid, 

 and phospho-tungstic acid. 



They give the biuret reaction (rose-red, with a trace of copper 

 sulphate and caustic potash or soda). 



Peptone is readily diffusible through animal membranes. The 

 utility of the formation of diffusible substances during digestion is 

 obvious. 



Proteoses. — These are the intermediate products in the hydrolysis 

 of native proteids into peptones. 



They are not coagulated by heat ; they are precipitated but not 

 ■coagulated by alcohol ; like peptone they give the biuret reaction. 

 They are precipitated by nitric acid, the precipitate being soluble on 



