Si8 
Theory  of  Indicators,  etc. 
( Am.  Jour.  Pbarm. 
\  November,  1904. 
proteids,  Osborne  and  Harris  estimated  the  percentages  of  ammonia 
and  so-called  basic  and  non-basic  nitrogen,  the  two  latter  being  dif- 
ferentiated by  the  fact  that  amido  bases  are  precipitated  by  means 
of  phosphotungstic  acid,  whilst  the  amido  acids  are  passed  through 
into  the  filtrate. 
In  carrying  out  comparative  series  of  experiments  on  the  nutritive 
value  of  certain  animal  and  vegetable  albumens,  we  have  frequently 
noted  far  greater  variations  in  the  alizarin  end  points  than  in  those 
of  phenolphthalein  and  phloroglucinvanillin  on  titration,  and  this  is 
of  especial  interest  taken  in  conjunction  with  Osborne's  work  on  the 
fractionation  of  the  products  of  decomposition  of  certain  proteids 
referred  to  above,  for  it  must  be  remembered  that  whilst  phloroglucin- 
vanillin is  sensitive  to  almost  all  the  NH2  groups  that  could  event- 
ually be  liberated  from  a  union  similar  to  that  existing  in  glycyl- 
glycin,  alizarin  is  only  sensitive  to  ammonia  and  those  amine  groups 
which  are  possessed  of  fairly  strong  basic  characteristics,  and  phenol- 
phthalein only  slightly  to  ammonia,  as  was  seen  in  a  previous  section 
of  this  article. 
It  is  highly  probable  that  the  range  of  the  various  periods 
between  the  titration  points  of  the  different  indicators  in  the  course 
of  peptic  or  tryptic  digestion  may  prove,  when  worked  out,  to 
afford  valuable  indications  regarding  the  type  of  combination  which 
each  individual,  freshly  exposed  amid  group  may  be  said  to  pos- 
sess; whether,  for  example,  it  is  associated  exclusively  with  carbon, 
to  which  only  hydrogen  is  attached,  or  to  what  extent  it  is  removed 
from  CO  groups,  or  whether  it  is  present  in  the  form  of  an  acid 
amid.  Unfortunately  time  does  not  permit  of  our  carrying  this 
question  further.  We  should  merely  wish  to  emphasize  the  value 
of  volumetric  methods  of  titration  in  following  the  progress  of  vari- 
ous digestive  processes,  and  any  reaction  in  which  the  hydrolysis  of 
proteids  or  less  complex  nitrogenous  compounds  is  concerned.  The 
small  amount  of  work  already  carried  out  in  this  direction  makes  it 
appear  probable  that  such  a  method  of  procedure,  when  taken  in 
conjunction  with  osmotic  pressure  and  other  physico-chemical  deter, 
minations,  may  be  expected  to  throw  some  light  on  the  methods  of 
grouping  of  the  various  atom  complexes  presesent  in  different  types 
of  proteid  molecules. 
From  analyses  carried  out  by  Dr.  Wheeler  in  the  laboratory  it 
appears  probable  that  each  advance  in  the  digestive  process  is 
