AmAp°riir;i907arm'}  Chemistry  of  the  Proteins.  171 
with  which  the  process  might  be  again  repeated  between  the 
terminal  amino  group  and  the  carboxyl  group  of  yet  another  mole- 
cule of  glycocoll,  giving  a  body 
NH2  CH2-CO-NH-CH2-CO-NH-CHo-COOH  (2) 
Such  products  receive  the  generic  name  "polypeptides";  when 
formed  from  two  molecules  of  an  amino  acid  they  are  dipeptides 
(glycylglycin,  1);  from  three  molecules,  tripeptides  (diglycyl-glycin, 
2),  etc.  The  following  may  be  quoted  as  illustrating  the  various 
methods  employed  for  bringing  about  this  type  of  reaction.  Glyco- 
coll is  allowed  to  interact  in  aqueous  alcoholic  solution  with  the  acid 
chloride  of  chloracetic  acid  : — 
C1CH2-C0C1  +  NH2-CH2  COOH  = 
C)CH2-CO-NH-CH2COOH  +  HQ 
and  the  chloroacetylglycin  so  formed  is  treated  with  aqueous  am- 
monia, when  the  chlorine  atom  is  replaced  by  an  amino  group  giving 
glycylglycin  (formula  1).  The  process  then  can  be  repeated  to  give 
tri-,  tetra-,  and  pentapeptides ;  but  it  becomes  tedious  for  the  prepa- 
ration of  very  complicated  substances,  which  are  obtained  by  a 
modification  of  the  process.  For  example,  pentaglycylglycin  (3)  is 
allowed  to  interact  with  the  acid  chloride  of  bromoisocapronyldi- 
glycilglycin  (4) 
(3)  COOH-CH0-NH(CO  CH,NH)4-CO-CHoNH|H 
\  L 
(4)  BrCH  (C4H9)-CO  (NH-CH2  CO),  NH-CH2.COjCl 
and  the  bromine  atom  in  this  body  is  then  replaced  by  an  amino 
group,  giving  leucyl-octaglycyl-glycin. 
NH2CH(C4H9)-CO(NH-CH2-CO)sNH-CH2COOH 
About  100  of  these  polypetides  have  been  prepared,  mostly  (on  ac- 
count of  expense)  derivatives  of  glycocoll,  alanine,  and  leucine  ;  but 
when  cost  and  trouble  have  not  to  be  considered  it  will  be  possible 
to  prepare  peptides  from  the  most  complicated  of  the  amino  acids. 
IDENTITY  OF  POLYPEPTIDES  WITH  PROTEINS. 
Some  of  the  polypeptides  have  proved  to  be  identical  with  certain 
degradation  products  of  the  peptones,  and  it  is  important  to  notice 
that  they  resemble  closely  in  their  properties  the  natural  proteins. 
