5 1 6  Theory  of  Indicators,  etc.  { 
(4)  This  range  increases  with  advancing  digestion  or  decomposi- 
tion as  does  the  phosphotungstic  nitrogen,  the  total  nitrogen  and 
chlorine  remaining  approximately  constant. 
VII.  TITRATION  OF  TRYPTIC  DIGESTION  PRODUCTS. 
A  series  of  digestion  experiments,  making  use  of  the  extracts  of 
pancreas  and  duodenum  of  human  beings  and  animals  which  were 
carried  out  with  a  different  purpose  in  view,  were  utilized  to  deter- 
mine the  effect  of  successive  stages  of  pancreatic  digestion  on  the 
end  points  of  indicators.  Whilst  a  constant  quantity  of  sodium 
carbonate  was  present  in  each  digest,  the  proportions  of  pancreatic 
extract  and  duodenal  extract  were  permitted  to  vary  within  wide 
limits.  Constant  weights  of  egg-white  and  plantose,  a  vegetable 
albumen,  were  employed,  and  the  period  during  which  they  were 
submitted  to  the  action  of  digestive  ferments  varied  from  four  to 
forty-eight  hours.  In  order  to  economize  space  it  has  been  found 
necessary  to  omit  the  tables,  but  it  may  be  said  that  in  each  case, 
with  increasing  concentration  or  extension  of  the  time  of  action,  an 
increased  quantity  of  nitrogenous  products  brought  into  solution 
was  invariably  accompanied  by  an  equivalent  increase  in  the  total 
range  of  titration  from  phloroglucinvanillin  to  phenolphthalein,  the 
influence  on  the  period  from  phloroglucinvanillin  to  alizarin  being 
more  marked  than  that  from  alizarin  to  phenolphthalein.  It  was 
also  observed  that  after  a  constant  amount  of  nitrogen  was  obtained, 
owing  to  the  proteids  being  entirely  in  solution,  further  digestion 
resulted  in  a  still  further  increase  in  the  titration  range,  the  phenol- 
phthalein end  point  requiring  slightly  more  alkali  or  less  acid,  and 
the  phloroglucinvanillin  end  point  more  acid  than  previously.  Alter 
allowing  for  the  influence  exerted  by  carbonic  acid  and  other  known 
causes  of  interference,  it  may  be  said  that  in  an  advanced  stage  of 
digestion  the  range  of  titration  is  frequently  almost  equal  to  the 
total  nitrogen ;  certainly  in  excess  of  one-half,  indicating  a  more 
advanced  stage  of  disintegration  than  was  observed  in. peptic  diges- 
tion experiments. 
VIII.  ON  THE  CONSTITUTION  OF  PROTEIDS. 
In  the  course  of  the  last  twenty  years  an  immense  amount  of 
research  has  been  devoted  to  the  solution  of  the  problem  of  the  con- 
stitution of  molecules  of  various  types  of  proteids  and  simpler 
