1178 



PROTEIDS. 



perature of the body into peptones, by the action of gastric 

 juice in an acid, or of pancreatic juice in an alkaline medium. 



All proteids in solution are precipitated by an excess of 

 strong alcohol. If the precipitant be rapidly removed they 

 are again soluble in water, but if the precipitated proteids are 

 subjected for some time to the action of the alcohol they are, 

 with the exception of albumoses and peptones, coagulated and 

 lose their solubility. 



CLASS VI. Albumoses and Peptones. 



When any of the proteids already described are submitted 

 to the digestive action of pepsin or trypsin, certain substances 

 are formed, in the earlier stages of the action, which are inter- 

 mediate between the proteid undergoing digestion and the pro- 

 teid product (peptone) which finally results from the action of 

 the enzymes. When the digestive fluid employed is pepsin in 

 presence of dilute (-2 p.c.) hydrochloric acid, a small portion of 

 the proteid may be at first converted into a form of ordinary 

 acid-albumin. 1 It is obtained by neutralizing a peptic digestive 

 mixture at an early stage of the digestion, and has been fre- 

 quently and almost usually confounded with the ' parapeptone ' 

 of Meissner. As will be explained later on, the two substances 

 are quite distinct forms of proteid. At a later stage of the 

 digestion the first-formed acid-albumin disappears, a consider- 

 able amount of parapeptone is formed and other products make 

 their appearance, which are known collectively under the name 

 of albumoses. By a more prolonged action of the pepsin a con- 

 siderable portion of these albumoses is further changed into the 

 final product peptones ; beyond this stage no further change 

 can be brought about by the action of pepsin. If trypsin be 

 employed in an alkaline solution (-25 p.c. Na 2 CO 3 ) the decom- 

 position of the proteid is much more complicated and profound. 

 Instead of acid-albumin a small amount of alkali-albumin makes 

 its appearance, together with more or less (see above, p. 1177) 

 of coagulable globulins in the earliest stages of the digestion. 

 Albumoses speedily make their appearance, to be somewhat 

 rapidly and it may be largely converted into peptones, of \vhich 

 some are in their turn partially, though never completely, 

 converted into leucine, tyrosine, and other less well-defined crys- 

 talline products. Similar products of the decomposition of 

 proteids may be obtained by the action of acids alone, in the 

 absence of all enzyme, preponderance of any one or more of 

 the products being dependent upon the concentration of the 

 acids, the temperature at which they are employed, and the 



J To this substance the name 'syntonin' was formerly applied; this term 

 is however most appropriately used to denote that form of acid-albumin which 

 results from the action of acids on myosin. (See above, p. 1170.) 



